Nonaqueous electrolyte battery, battery pack and vehicle

ABSTRACT

A nonaqueous electrolyte battery includes a negative electrode including a current collector and a negative electrode active material having a Li ion insertion potential not lower than 0.4V (vs. Li/Li + ). The negative electrode has a porous structure. A pore diameter distribution of the negative electrode as determined by a mercury porosimetry, which includes a first peak having a mode diameter of 0.01 to 0.2 μm, and a second peak having a mode diameter of 0.003 to 0.02 μm. A volume of pores having a diameter of 0.01 to 0.2 μm as determined by the mercury porosimetry is 0.05 to 0.5 mL per gram of the negative electrode excluding the weight of the current collector. A volume of pores having a diameter of 0.003 to 0.02 μm as determined by the mercury porosimetry is 0.0001 to 0.02 mL per gram of the negative electrode excluding the weight of the current collector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/369,048, filed Feb. 8, 2012, which is a continuation of U.S.application Ser. No. 13/151,466, filed Jun. 2, 2011, which is acontinuation of and claims the benefit of priority under 35 U.S.C. §120from U.S. Ser. No. 12/897,818, filed Oct. 5, 2010, which is acontinuation of U.S. Ser. No. 12/691,365, filed Jan. 21, 2010, which isa continuation application of U.S. Ser. No. 11/261,538, filed Oct. 31,2005, and is based upon and claims the benefit of priority from priorJapanese Patent Application No. 2005-199445, filed Jul. 7, 2005, theentire contents of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nonaqueous electrolyte battery, abattery pack using the nonaqueous electrolyte battery, and a vehiclehaving the battery pack mounted thereto.

2. Description of the Related Art

Vigorous research is being conducted on a electrode in an attempt todevelop a high energy density battery.

The nonaqueous electrolyte battery is required to satisfy variouscharacteristics depending on the use of the battery. For example, it isdesirable for the nonaqueous electrolyte battery used as a power sourceof a digital camera to achieve the discharge not lower than about 3C,and for the nonaqueous electrolyte battery mounted to a vehicle such asa hybrid automobile to achieve the discharge not lower than about 10C.Such being the situation, the nonaqueous electrolyte battery used in thefields exemplified above is required to exhibit an excellentcharge-discharge cycle life when the charge-discharge is repeated undera large current.

The nonaqueous electrolyte battery available on the market nowadayscomprises a positive electrode in which a lithium-transition metalcomposite oxide is used as the positive electrode active material and anegative electrode in which a carbonaceous material is used as thenegative electrode active material. In general, Co, Mn, Ni, etc. areused as the transition metals contained in the lithium-transition metalcomposite oxide used as the positive electrode active material.

In recent years, a nonaqueous electrolyte battery in whichlithium-titanium oxide having a high Li ion insertion potential,compared with the carbonaceous material, is used as a negative electrodeactive material has been put to the practical use. The lithium-titaniumoxide is small in change of volume accompanying the charge-dischargeoperation of the secondary battery, and, thus, permits the nonaqueouselectrolyte battery using the lithium-titanium oxide as the negativeelectrode active material to be excellent in the charge-discharge cyclecharacteristics, compared with the nonaqueous electrolyte battery usingthe carbonaceous material as the negative electrode active material.Particularly, it is desirable to use lithium titanate having a spinelstructure as the negative electrode active material.

For example, Japanese Patent Disclosure (Kokai) No. 09-199179 disclosesa nonaqueous electrolyte battery comprising lithium titanate, which issmall in change of volume during the charge-discharge operation of thesecondary battery, as the negative electrode active material. It istaught that the nonaqueous electrolyte battery is small in change ofvolume, and that the short circuiting and the decrease of the batterycapacity accompanying the swelling of the electrode are unlikely to takeplace.

On the other hand, Japanese Patent Disclosure (Kokai) No. 2005-72008discloses a negative electrode active material formed of vanadium oxiderepresented by Li_(x)M_(y)V_(z)O_(2+d). It is disclosed that negativeelectrode active material has pores having a pore diameter of 0.1 to 10μm and that the pore volume per unit weight of the negative electrodeactive material is 10⁻³ cc/g to 0.8 cc/g.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a nonaqueouselectrolyte battery excellent in the charge-discharge cycle life, abattery pack using the nonaqueous electrolyte battery, and a vehicleusing the battery pack.

According to a first aspect of the present invention, there is provideda nonaqueous electrolyte battery, comprising:

a positive electrode;

a negative electrode including a current collector and a negativeelectrode layer being supported by the current collector, and thenegative electrode layer containing a negative electrode active materialhaving a Li ion insertion potential not lower than 0.4V (vs. Li/Li⁺);and

a nonaqueous electrolyte;

wherein:

the negative electrode has a porous structure;

a pore diameter distribution of the negative electrode as determined bya mercury porosimetry, which includes a first peak having a modediameter falling within a range of 0.01 to 0.2 μm, and a second peakhaving a mode diameter falling within a range of 0.003 to 0.02 μm;

a volume of pores having a diameter of 0.01 to 0.2 μm as determined bythe mercury porosimetry is 0.05 to 0.5 mL per gram of the negativeelectrode excluding the weight of the current collector; and

a volume of pores having a diameter of 0.003 to 0.02 μm as determined bythe mercury porosimetry is 0.0001 to 0.02 mL per gram of the negativeelectrode excluding the weight of the current collector.

According to a second aspect of the present invention, there is provideda nonaqueous electrolyte battery, comprising:

a positive electrode,

a negative electrode including a current collector and a negativeelectrode layer being supported by the current collector, and thenegative electrode layer containing a lithium-titanium oxide; and

a nonaqueous electrolyte;

wherein:

the negative electrode has a porous structure;

a pore diameter distribution of the negative electrode as determined bya mercury porosimetry, which includes a first peak having a modediameter falling within a range of 0.01 to 0.2 μm, and a second peakhaving a mode diameter falling within a range of 0.003 to 0.02 μm;

a volume of pores having a diameter of 0.01 to 0.2 μm as determined bythe mercury porosimetry is 0.05 to 0.5 mL per gram of the negativeelectrode excluding the weight of the current collector; and

a volume of pores having a diameter of 0.003 to 0.02 μm as determined bythe mercury porosimetry is 0.0001 to 0.02 mL per gram of the negativeelectrode excluding the weight of the current collector.

According to a third aspect of the present invention, there is provideda battery pack comprising nonaqueous electrolyte batteries, eachnonaqueous electrolyte battery comprising:

a positive electrode;

a negative electrode including a current collector and a negativeelectrode layer being supported by the current collector, the negativeelectrode layer containing a negative electrode active material having aLi ion insertion potential not lower than 0.4V (vs. Li/Li⁺); and

a nonaqueous electrolyte;

wherein:

the negative electrode has a porous structure;

a pore diameter distribution of the negative electrode as determined bya mercury porosimetry, which includes a first peak having a modediameter falling within a range of 0.01 to 0.2 μm, and a second peakhaving a mode diameter falling within a range of 0.003 to 0.02 μm;

a volume of pores having a diameter of 0.01 to 0.2 μm as determined bythe mercury porosimetry is 0.05 to 0.5 mL per gram of the negativeelectrode excluding the weight of the current collector; and

a volume of pores having a diameter of 0.003 to 0.02 μm as determined bythe mercury porosimetry is 0.0001 to 0.02 mL per gram of the negativeelectrode excluding the weight of the current collector.

According to a fourth aspect of the present invention, there is provideda vehicle comprising a battery pack including nonaqueous electrolytebatteries, each nonaqueous electrolyte battery comprising:

a positive electrode;

a negative electrode including a current collector and a negativeelectrode layer being supported by the current collector, and thenegative electrode layer containing a negative electrode active materialhaving a Li ion insertion potential not lower than 0.4V (vs. Li/Li⁺);and

a nonaqueous electrolyte;

wherein:

the negative electrode has a porous structure;

a pore diameter distribution of the negative electrode as determined bya mercury porosimetry, which includes a first peak having a modediameter falling within a range of 0.01 to 0.2 μm, and a second peakhaving a mode diameter falling within a range of 0.003 to 0.02 μm;

a volume of pores having a diameter of 0.01 to 0.2 μm as determined bythe mercury porosimetry is 0.05 to 0.5 mL per gram of the negativeelectrode excluding the weight of the current collector; and

a volume of pores having a diameter of 0.003 to 0.02 μm as determined bythe mercury porosimetry is 0.0001 to 0.02 mL per gram of the negativeelectrode excluding the weight of the current collector.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross sectional view schematically showing the constructionof a flat type nonaqueous electrolyte battery according to a firstembodiment of the present invention;

FIG. 2 is a cross sectional view showing in detail in a magnifiedfashion the construction of the circular region A of the nonaqueouselectrolyte battery shown in FIG. 1;

FIG. 3 is an oblique view, partly broken away, schematically showing theconstruction of another nonaqueous electrolyte battery according to thefirst embodiment of the present invention;

FIG. 4 is a cross sectional view showing in a magnified fashion theconstruction of region B of the nonaqueous electrolyte battery shown inFIG. 3;

FIG. 5 is an oblique view showing in a dismantled fashion theconstruction of the battery pack according to a second embodiment of thepresent invention;

FIG. 6 is a block diagram showing the electric circuit of the batterypack shown in FIG. 5;

FIG. 7 is a graph showing the pore diameter distribution as determinedby the mercury porosimetry in the negative electrode for Example 3; and

FIG. 8 is a graph showing in a magnified fashion that region of the porediameter distribution shown in FIG. 7 which is in the vicinity of 0.01μm of the diameter.

DETAILED DESCRIPTION OF THE INVENTION

A negative electrode active material having a Li ion insertion potentialnot lower than 0.4V (vs. Li/Li⁺) is small in the change of volumeaccompanying the charge-discharge operation of the battery, i.e., theabsorption and release of lithium ions. The electrode containing thisparticular active material is unlikely to be swollen. On the other hand,the negative electrode containing as a negative electrode activematerial a carbonaceous material that has already been put to themarket, such as graphite, exhibits several percent of expansion andshrinkage of the volume in accordance with the charge-dischargeoperation of the battery. As a result, in the case of using, forexample, graphite as the negative electrode active material, thenonaqueous electrolyte is diffused in accordance with expansion andshrinkage of the electrode. It follows that the impregnation of theelectrode with a nonaqueous electrolyte tends to be promoted.Alternatively, the concentration of the electrolyte such as a lithiumsalt tends to be made uniform. It has been found, however, that theelectrode containing the lithium-titanium oxide, which is small in thechange of volume, is markedly poor in the impregnation capability of theelectrode with the nonaqueous electrolyte. Particularly, in the case ofmanufacturing a large battery that is mounted to, for example, avehicle, the poor impregnation capability of the electrode with thenonaqueous electrolyte was found to lower the productivity. In addition,the poor impregnation capability of the electrode was also found tomarkedly lower the battery performance, particularly, thecharge-discharge cycle life.

Under the circumstances, the present inventors insistently stirredstrongly the slurry in the manufacturing stage of the negative electrodein an attempt to manufacture a negative electrode exhibiting a Li ioninsertion potential not lower than 0.4V (vs. Li/Li⁺), i.e., a negativeelectrode absorbing-releasing lithium ions under potentials nobler by0.4V or more relative to the lithium metal potential. As a result, itwas possible to suppress the agglomeration of particles to permit theparticles to be dispersed uniformly, leading to the successfulmanufacture of the porous negative electrode having a pore diameterdistribution having a sharp peak within a diameter range of 0.01 to 0.2μm and a sub-peak within a diameter range of 0.003 to 0.02 μm. Thepresent inventors have further continued the research to find thatconstructions (A) and (B) given below are highly effective for markedlyimproving the impregnation capability of the negative electrode with thenonaqueous electrolyte to improve not only the productivity but also thelarge current characteristics and the charge-discharge cycle life of thebattery:

(A) The volume of the first pores having a diameter of 0.01 to 0.2 μmshould be 0.05 to 0.5 mL per gram of the negative electrode excludingthe weight of the negative electrode current collector.

(B) The volume of the second pores having a diameter of 0.003 to 0.02 μmshould be 0.0001 to 0.02 mL per gram of the negative electrode excludingthe weight of the negative electrode current collector.

Since fine pores are uniformly distributed in the negative electrode,the high impregnation capability of the negative electrode can beretained without lowering the electrode density. As a result, it ispossible to increase the density of the electrode, leading to a highcapacity of the battery.

Further, in the case of using a positive electrode containing the spineltype lithium-manganese-nickel composite oxide as the positive electrodeactive material together with the negative electrode noted above, it isalso possible to increase the voltage of the battery. Alternatively, inthe case of using a lithium-phosphorus composite oxide having theolivine structure such as Li_(x)FePO₄, Li_(x)Fe_(1-x)Mn_(y)PO₄,Li_(x)VPO₄F, or Li_(x)CoPO₄, where each of x and y falls within a rangeof 0 to 1, i.e., 0≦x≦1; 0≦y≦1, it is possible to realize a nonaqueouselectrolyte battery excellent in the thermal stability.

Some embodiments of the present invention will now be described withreference to the accompanying drawings. Incidentally, the commonconstituents of the invention are denoted by the same reference numeralsin the accompanying drawings to omit the overlapping description. Also,the accompanying drawings are schematic drawings that are simplyintended to facilitate the description and understanding of theinvention. It is possible for the shape, the size, the ratio, etc. shownin the drawing to differ from those of the actual battery. Of course,the design relating to the size, shape, etc. can be changedappropriately in view of the description given below and the knowntechnology.

First Embodiment

An example of the construction of the unit cell, i.e., nonaqueouselectrolyte battery, according to the first embodiment of the presentinvention will now be described with reference to FIGS. 1 and 2.Specifically, FIG. 1 is a cross sectional view schematically showing theconstruction of a flat type nonaqueous electrolyte battery according toa first embodiment of the present invention, and FIG. 2 is a crosssectional view schematically showing in detail in a magnified fashionthe construction of the circular region A of the nonaqueous electrolytebattery shown in FIG. 1.

As shown in FIG. 1, a flat type wound electrode group 6 is housed in acase 7. The wound electrode group 6 is formed of a laminate structurecomprising a positive electrode 3, a negative electrode 4, and aseparator 5 interposed between the positive electrode 3 and the negativeelectrode 4. The electrode group 6 is obtained by spirally winding thelaminate structure noted above. Further, a nonaqueous electrolyte isretained by the wound electrode group 6.

As shown in FIG. 2, the negative electrode 4 is positioned to constitutethe outermost circumferential region of the wound electrode group 6.Also, the positive electrode 3 and the negative electrode 4 arealternately laminated one upon the other with the separator 5 interposedtherebetween. For example, the separator 5, the positive electrode 3,the separator 5, the negative electrode 4, the separator 5, the positiveelectrode 3 and the separator 5 are laminated one upon the other in theorder mentioned. The negative electrode 4 comprises a negative electrodecurrent collector 4 a and a negative electrode activematerial-containing layer 4 b supported by the negative electrodecurrent collector 4 a. The negative electrode active material-containinglayer 4 b is porous. In that region of the negative electrode 4 whichconstitutes the outermost circumferential region, the negative electrodeactive material-containing layer 4 b is formed on one surface of thenegative electrode current collector 4 a. On the other hand, thepositive electrode 3 comprises a positive electrode current collector 3a and a positive electrode active material-containing layer 3 bsupported by the positive electrode current collector 3 a.

As shown in FIG. 1, a band-like positive electrode terminal 1 iselectrically connected to the positive electrode current collector 3 ain the vicinity of the outer circumferential region of the woundelectrode group 6. On the other hand, a band-like negative electrodeterminal 2 is electrically connected to the negative electrode currentcollector 4 a in the vicinity of the outer circumferential region of thewound electrode group 6. Further, the tip portions of the positiveelectrode terminal 1 and the negative electrode terminal 2 are withdrawnto the outside of the case 7 via the same side of the case 7.

The negative electrode, the nonaqueous electrolyte, the positiveelectrode, the separator, the case, the positive electrode terminal andthe negative electrode terminal will now be described in detail.

1) Negative Electrode

As described previously, the negative electrode active material exhibitsa Li ion insertion potential not lower than 0.4V (vs. Li/Li⁺). In thecase of using an active material capable of absorbing lithium or lithiumions at a potential baser than 0.4V (vs. Li/Li⁺), e.g., graphite,lithium metal, or the vanadium oxide represented byLi_(x)M_(y)V_(z)O_(2+d), which is disclosed in Japanese PatentDisclosure (Kokai) No. 2005-72008 referred to previously, the reducingreaction of the nonaqueous electrolyte proceeds excessively on thesurface of the active material if the diameter of the particles formingthe negative electrode is diminished to markedly lower the batterycharacteristics, particularly, the output characteristics and thecharge-discharge cycle life. The particular phenomenon is caused toappear prominently, if the diameter of the active material particlesabsorbing lithium or lithium ions at a potential baser than 0.2V (vs.Li/Li⁺) is set smaller than 1 μm. It follows that it is desirable forthe Li ion insertion potential of the negative electrode active materialto be not lower than 0.4V (vs. Li/Li⁺) and for the upper limit of the Liion insertion potential of the negative electrode active material to beset at 3V (vs. Li/Li⁺), preferably at 2V (vs. Li/Li⁺).

The negative electrode active material having the Li ion insertionpotential falling within a range of 0.4 to 3V (vs. Li/Li⁺) includes ametal oxide, a metal sulfide, a metal nitride or an alloy.

The metal oxide that can be used as the negative electrode activematerial includes, for example, a titanium-containing metal compositeoxide, a tin-containing oxide such as SnB_(0.4)P_(0.6)O_(3.1) or SnSiO₃,a silicon-containing oxide such as SiO, and tungsten-containing oxidesuch as WO₃. Particularly, it is desirable to use a titanium-containingmetal composite oxide as the negative electrode active material.

The titanium-containing metal composite oxide noted above includes, forexample, a titanium-based oxide that does not contain lithium in thestage of synthesizing the oxide, lithium-titanium oxide, and alithium-titanium composite oxide obtained by substituting a foreignelement for a part of the constituting elements of the lithium-titaniumoxide.

The lithium-titanium oxide includes, for example, lithium titanatehaving a spinel structure, e.g., Li_(4+x)Ti₅O₁₂ (0≦x≦3), and lithiumtitanate having a ramsdellite structure, e.g., Li_(2+y)Ti₃O₇ (0≦y≦3).

The titanium-based oxide noted above includes, for example, TiO₂ and ametal composite oxide containing Ti and at least one element selectedfrom the group consisting of P, V, Sn, Cu, Ni, Co and Fe. It isdesirable for TiO₂ to be of anatase type and to have a low crystallinitycaused by a heat treating temperature of 300 to 500° C. The metalcomposite oxide containing Ti and at least one element selected from thegroup consisting of P, V, Sn, Cu, Ni, Co and Fe includes, for example,TiO₂—P₂O₅, TiO₂—V₂O₅, TiO₂—P₂O₅—SnO₂, and TiO₂—P₂O₅-MeO (Me denoting atleast one element selected from the group consisting of Cu, Ni, Co andFe). To be more specific, it is desirable for the micro structure of themetal composite oxide to include a crystal phase and an amorphous phaseor a single phase formed of an amorphous phase. The particular microstructure makes it possible to improve markedly the charge-dischargecycle performance of the nonaqueous electrolyte battery. Particularly,it is desirable to use lithium-titanium oxide and a metal compositeoxide containing Ti and at least one element selected from the groupconsisting of P, V, Sn, Cu, Ni, Co and Fe.

The metal sulfide used as the negative electrode active materialincludes, for example, a Ti-containing sulfide such as TiS₂, amolybdenum-containing sulfide such as MoS₂ and iron-containing sulfidesuch as FeS, FeS₂, Li_(x)FeS₂ (0≦x≦4).

The metal nitride used as the negative electrode active materialincludes, for example, lithium-containing nitrides such as (Li, Me)₃N(where Me denotes a transition metal element.

It is desirable for the negative electrode active material to have anaverage particle diameter not larger than 1 μm. If the negativeelectrode active material has an average particle diameter exceeding 1μm, it may be difficult to permit the negative electrode to have poreshaving the diameter falling within the range specified in thisembodiment of the present invention. If the average particle diameter isexcessively small, however, the distribution of the nonaqueouselectrolyte is inclined on the negative electrode, with the result thatthe nonaqueous electrolyte tends to be depleted on the positiveelectrode. Such being the situation, it is desirable for the lower limitof the average particle diameter in the negative electrode activematerial to be set at 0.001 μm.

It is desirable for the negative electrode active material to have anaverage particle diameter not larger than 1 μm and to have a specificsurface area falling within a range of 5 to 50 m²/g as determined by theBET method utilizing the N₂ adsorption. Where the negative electrodeactive material has the average particle diameter and the specificsurface area noted above, the pore diameter distribution in the negativeelectrode can be controlled easily to fall within the range specified inthe first embodiment of the present invention to make it possible toenhance the impregnation capability of the negative electrode with thenonaqueous electrolyte.

The reasons for defining the pore diameter distribution in the negativeelectrode to fall within the range referred to above will now bedescribed.

It is desirable for the pores to consist of open cells formed inside theporous material and extending to reach the surface of the porousmaterial (see “Iwanami's Dictionary of Physics and Chemistry 5th EditionCD-ROM). The term “mode diameter” denotes the peak top of a porediameter distribution curve in a graph in which pore diameter is plottedon the abscissa and the frequency is plotted on the ordinate.

<First Peak>

The first peak is ascribed to the pores formed by the constituents ofthe negative electrode such as the active material particles, theconductive agent and the binder.

In the first embodiment of the present invention, the mode diameter ofthe first peak of the pore diameter distribution as determined by themercury porosimetry is set not to exceed 0.2 μm to promote theimpregnation of the negative electrode with the nonaqueous electrolyteperformed by the capillary action of the pore. At the same time, thelower limit of the mode diameter is set at 0.01 μm. It should be notedin this connection that the by-products (organic materials or inorganicmaterials) formed by the reaction with the electrolyte is deposited onthe surface of the negative electrode active material or on the surfaceof the negative electrode conductive agent. If the mode diameter of thefirst peak is smaller than 0.01 μm, the pores are closed by the growthof the by-product to lower the capability of retaining the nonaqueouselectrolyte of the negative electrode, with the result that thecharge-discharge cycle characteristics of the battery are lowered. Underthe circumstances, it is desirable for the mode diameter of the firstpeak to fall within a range of 0.01 to 0.2 μm, more desirably to fallwithin a range of 0.02 to 0.1 μm.

The volume of the first pores, as determined by the mercury porosimetry,having the pore diameters falling within a range of 0.01 to 0.2 μm fallswithin a range of 0.05 to 0.5 mL per gram of the negative electrodeexcluding the weight of the negative electrode current collector. Fordetermining the pore volume per unit weight of the negative electrode,the weight of the negative electrode current collector is excluded fromthe calculation. As described herein later, the negative electrodecurrent collector is formed of a nonporous conductive substrate such asan aluminum foil. Clearly, the negative electrode current collector isirrelevant to the pore diameter distribution. Such being the situation,it is reasonable to subtract the weight of the negative electrodecurrent collector from the weight of the negative electrode in order toobtain the effective pore diameter distribution within the negativeelectrode. If the specific pore volume is smaller than 0.05 mL/g, thenonaqueous electrolyte is depleted within the negative electrode tolower the charge-discharge cycle characteristics of the battery. On theother hand, if the specific pore volume exceeds 0.5 mL/g, thedistribution of the nonaqueous electrolyte is inclined on the negativeelectrode to bring about depletion of the nonaqueous electrolyte in thepositive electrode. It is more desirable for the specific pore volumenoted above to fall within a range of 0.1 to 0.3 mL/g.

It is desirable for the surface area of the first pores having adiameter of 0.01 to 0.2 μm, as determined by the mercury porosimetry,per gram of the negative electrode excluding the weight of the negativeelectrode current collector to fall within a range of 5 to 50 m². Theweight of the negative electrode current collector is excluded from thecalculation of the surface area of the pores per gram of the negativeelectrode because the negative electrode current collector is nonporousand, thus, it is unreasonable to include the weight of the negativeelectrode current collector in the calculation noted above, as pointedout above. It should be noted that if the specific surface area of thefirst pores noted above is smaller than 5 m²/g, the effect of promotingthe impregnation of the negative electrode with the nonaqueouselectrolyte tends to be diminished. On the other hand, if the specificsurface area of the first pores noted above exceeds 50 m²/g, it isdifficult to increase the electrode density to lower the energy density.In addition, it is possible for the electron conductivity to be loweredto lower the output performance. It is more desirable for the specificsurface area of the first pores noted above to fall within a range of 7to 30 m²/g.

<Second Peak>

The second peak is ascribed to the pores of the negative electrodeactive material itself.

If the negative electrode has a pore diameter distribution such that themode diameter of a second peak falls within a range of 0.003 to 0.02 μmas determined by the mercury porosimetry, the impregnation capability ofthe negative electrode with the nonaqueous electrolyte is markedlyimproved to improve prominently the large current characteristics. Itshould be noted that the presence of the second peak in the porediameter distribution permits effectively promoting the capillary actionperformed by the pores. However, if the mode diameter of the second peakis smaller than 0.003 μm, the dispersion capability of the electrolytehaving a large molecular weight is lowered to give rise to thepossibility that the impregnation capability of the negative electrodenoted above may be lowered. Such being the situation, it is desirablefor the lower limit of the mode diameter of the second peak to be set at0.003 μm. It is more desirable for the mode diameter of the second peakof the pore diameter distribution to fall within a range of 0.005 to0.015 μm.

The volume of the second pores having a diameter of 0.003 to 0.02 μm asdetermined by the mercury porosimetry per gram of the negative electrodeexcluding the negative electrode current collector should fall within arange of 0.0001 to 0.02 mL. The negative electrode current collector isexcluded from the calculation of the volume of the pores per gram of thenegative electrode, as described previously. If the specific pore volumenoted above is smaller than 0.0001 mL/g, it is impossible to obtain asufficient effect of improving the impregnation capability of thenegative electrode with the nonaqueous electrolyte. On the other hand,if the specific pore volume noted above is larger than 0.02 mL/g, thestrength of the negative electrode active material is lowered. As aresult, the particles of the negative electrode active material tend tobe collapsed in the pressing stage of the electrode to lower thecharge-discharge cycle performance and the high rate characteristics ofthe battery. It is more desirable for the pore volume per gram of thenegative electrode to fall within a range of 0.0005 to 0.01 mL/g.

It is desirable for the surface area of the second pores having adiameter of 0.003 to 0.02 μm, as determined by the mercury porosimetry,per gram of the negative electrode excluding the negative electrodecurrent collector to fall within a range of 0.1 to 10 m². The weight ofthe negative electrode current collector is excluded from thecalculation of the surface area of the pores per unit weight of thenegative electrode because the negative electrode current collector isgenerally formed of a nonporous material such as an aluminum foil, aspointed out previously. If the specific surface area of the second poresis smaller than 0.1m²/g, it is impossible to obtain a sufficient effectof improving the impregnation capability of the negative electrode withthe nonaqueous electrolyte. On the other hand, if the specific surfacearea of the second pores exceeds 10 m²/g, it is difficult to increasethe electrode density and, thus, the energy density tends to be lowered.It is more desirable for the specific surface area of the second poresto fall within a range of 0.2 to 2 m²/g.

It is desirable for the pore volume as determined by the mercuryporosimetry per gram of the negative electrode excluding the negativeelectrode current collector to fall within a range of 0.1 to 1 mL. Theweight of the negative electrode current collector is excluded from thecalculation of the volume of the pores per unit weight of the negativeelectrode because the negative electrode current collector is generallyformed of a nonporous material, as pointed out previously. If thespecific pore volume of the negative electrode is not smaller than 0.1mL/g, it is possible for the negative electrode to retain a sufficientlylarge amount of the nonaqueous electrolyte. However, if the specificpore volume is smaller than 0.1 mL/g, the nonaqueous electrolyte tendsto be depleted within the negative electrode to lower thecharge-discharge cycle characteristics of the battery. It should also benoted in respect of the limitation that the specific pore volume in thenegative electrode should not exceed 1 mL/g that, if the specific porevolume is excessively large, the distribution of the nonaqueouselectrolyte tends to be inclined on the negative electrode to bringabout depletion of the electrolyte on the positive electrode. It is moredesirable for the pore volume per unit weight of the negative electrodeto fall within a range of 0.2 to 0.5 mL/g.

It is desirable for the surface area of the pores as determined by themercury porosimetry per gram of the negative electrode excluding thenegative electrode current collector to fall within a range of 5 to 50m². The weight of the negative electrode current collector is excludedfrom the calculation of the surface area of the pores per unit weight ofthe negative electrode because the negative electrode current collectoris generally formed of a nonporous material, as pointed out previously.If the specific surface area of the pores is smaller than 5 m²/g, theaffinity between the negative electrode and the nonaqueous electrolyteis lowered, with the result that it is possible for the pore diameterdistribution described previously to fail to produce a sufficient effectof improving the impregnation capability of the negative electrode withthe nonaqueous electrolyte. On the other hand, if the specific surfacearea noted above exceeds 50 m²/g, the distribution of the nonaqueouselectrolyte tends to be inclined on the negative electrode, with theresult that shortage of the nonaqueous electrolyte is brought about inthe positive electrode, resulting in failure to improve thecharge-discharge cycle characteristics of the battery. It is moredesirable for the specific surface area of the pores to fall within arange of 7 to 30 m²/g.

It is desirable for the porosity of the negative electrode excluding thenegative electrode current collector to fall within a range of 20 to50%. If the porosity of the negative electrode falls within the rangenoted above, the affinity between the negative electrode and thenonaqueous electrolyte is improved. In addition, it is possible toobtain a negative electrode having a high density. It is more desirablefor the porosity of the negative electrode to fall within a range of 25to 40%.

It is desirable for the density of the negative electrode to be notlower than 2 g/cc. If the density of the negative electrode is lowerthan 2 g/cc, it may be difficult to obtain a negative electrode havingthe pore diameter distribution described previously. It is moredesirable for the density of the negative electrode to fall within arange of 2 to 2.5 g/cc.

It is desirable for the current collector of the negative electrode tobe formed of aluminum foil or aluminum alloy foil. It is also desirablefor the negative electrode current collector to have an average crystalgrain size not larger than 50 μm. In this case, the mechanical strengthof the current collector can be drastically increased so as to make itpossible to increase the density of the negative electrode by applyingthe pressing under a high pressure to the negative electrode. As aresult, the battery capacity can be increased. Also, since it ispossible to prevent the dissolution and corrosion deterioration of thenegative electrode current collector over a long over-discharge cycleunder an environment of a high temperature not lower than, for example,40° C., it is possible to suppress the elevation in the impedance of thenegative electrode. Further, it is possible to improve the high-ratecharacteristics, the rapid charging properties, and the charge-dischargecycle characteristics of the battery. It is more desirable for theaverage crystal grain size of the negative electrode current collectorto be not larger than 30 μm, furthermore desirably, not larger than 5μm.

The average crystal grain size can be obtained as follows. Specifically,the texture of the current collector surface is observed with anelectron microscope so as to obtain the number n of crystal grainspresent within an area of 1 mm×1 mm. Then, the average crystal grainarea S is obtained from the formula “S=1×10⁶/n (μm²)”, where n denotesthe number of crystal grains noted above. Further, the average crystalgrain size d (μm) is calculated from the area S by formula (A) givenbelow:

d=2(S/π)^(1/2)  (A)

The aluminum foil or the aluminum alloy foil having the average crystalgrain size not larger than 50 μm can be complicatedly affected by manyfactors such as the composition of the material, the impurities, theprocess conditions, the history of the heat treatments and the heatingconditions such as the annealing conditions, and the crystal grain sizecan be adjusted by an appropriate combination of the factors noted aboveduring the manufacturing process.

It is desirable for the aluminum foil or the aluminum alloy foil to havea thickness not larger than 20 μm, more desirably not larger than 15 μm.Also, it is desirable for the aluminum foil to have a purity not lowerthan 99%. It is desirable for the aluminum alloy to contain anotherelement such as magnesium, zinc or silicon. On the other hand, it isdesirable for the amount of the transition metal such as iron, copper,nickel and chromium contained in the aluminum alloy to be not largerthan 1%.

It is possible for the negative electrode active material-containinglayer to contain a conductive agent. The conductive agent includes, forexample, a carbon material, a metal powder such as an aluminum powder,and a conductive ceramic material such as TiO. The carbon material usedas the conductive agent includes, for example, acetylene black, carbonblack, coke, a carbon fiber and graphite. It is more desirable for thecarbon material to include, for example, coke subjected to a heattreatment at 800 to 2,000° C. and having an average particle diameternot larger than 10 μm, graphite, a TiO powder, and a carbon fiber havingan average particle diameter not larger than 1 μm. It is desirable forthe carbon material to have at least 10 m²/g of the BET specific surfacearea as determined by the N₂ adsorption.

It is also possible for the negative electrode activematerial-containing layer to contain a binder. The binder includes, forexample, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF),a fluorinated rubber, styrene-butadiene rubber and a core shell binder.

Concerning the mixing ratio of the negative electrode active material,the negative electrode conductive agent, and the binder, it is desirablefor the negative electrode active material to be used in an amount notsmaller than 70% by weight and not larger than 96% by weight, for thenegative electrode conductive agent to be used in an amount not smallerthan 2% by weight and not larger than 28% by weight, and for the binderto be used in an amount not smaller than 2% by weight and not largerthan 28% by weight. If the mixing amount of the negative electrodeconductive agent is smaller than 2% by weight, the current collectingperformance of the negative electrode porous layer may be lowered topossibly lower the large current characteristics of the nonaqueouselectrolyte battery. Also, if the mixing amount of the binder is smallerthan 2% by weight, the bonding between the negative electrode porouslayer and negative electrode current collector may be lowered topossibly lower the charge-discharge cycle characteristics of thenonaqueous electrolyte battery. On the other hand, it is desirable forthe mixing amount of each of the negative electrode conductive agent andthe binder to be not larger than 28% by weight in view of theimprovement in the capacity of the nonaqueous electrolyte battery.

The negative electrode can be prepared by, for example, coating anegative electrode current collector with a slurry prepared bysuspending a negative electrode active material, a negative electrodeconductive agent and a binder in a solvent that is used widely, followedby drying the current collector coated with the slurry to form anegative electrode porous layer and subsequently pressing the negativeelectrode porous layer. In manufacturing the negative electrode, theslurry is prepared as follows. In the first step, a negative electrodeactive material, a negative electrode conductive agent and a binder areput in a small amount of the solvent. These materials are kneaded with,for example, a planetary mixer under the state of a high solid materialratio, i.e., the state that the ratio of the solid materials includingthe negative electrode active material, the negative electrodeconductive agent and the binder to the solvent is high, to apply astrong shearing force to the mixture and, thus, to disperse uniformlythe solid components of the mixture. It should be noted that, if thesolid material ratio is not sufficiently high, the shearing force isdecreased, with the result that the agglomerated negative electrodeactive material is not pulverized sufficiently, resulting in failure forthe solid components to be dispersed uniformly. The kneading processnoted above is rendered more important with increase in the fineness ofthe particle diameter of the negative electrode active material. Thekneading process is particularly important in the case of handling theparticles having an average particle diameter not larger than 1 μm.After the mixture is kneaded sufficiently under the state of a highratio of the solid components, the solid component ratio is graduallylowered while adding a solvent to adjust the slurry at a viscosityadapted for the coating. The slurry adjusted at a viscosity adapted forthe coating is mixed sufficiently by using a bead mill including ceramicballs used as a mixing medium. In this mixing step, the edges of theparticles of the active material are scraped off to smoothen the surfaceof the particles of the active material. As a result, the negativeelectrode active material can be loaded at a high loading density toshift the pore diameter distribution toward the small diameter, therebymaking it possible to obtain a negative electrode having the porediameter distribution specified in the this embodiment of the presentinvention. The ceramic balls used in the bead mill can be formed ofvarious materials such as glass, alumina, mullite, and silicon nitride.In view of the wear resistance and the impact resistance, it isdesirable to use zirconia balls as the ceramic balls. It is desirablefor the ball to have a diameter of 0.5 to 5 mm. If the diameter of theball is smaller than 0.5 mm, it is difficult to obtain a sufficientlylarge impact force. On the other hand, if the diameter of the ball islarger than 5 mm, the contact area among the adjacent balls isexcessively diminished to lower the kneading capability of the balls. Itis more desirable for the balls to have a diameter falling within arange of 1 to 3 mm.

The negative electrode current collector is coated with the slurry thusobtained, followed by drying the slurry and subsequently pressing thenegative electrode current collector coated with the slurry by a rollpress machine to finish manufacture of the negative electrode. It isdesirable for the roll temperature to fall within a range of 40 to 180°C. If the roll temperature is excessively low, the conductive agenthaving a specific gravity lower than that of the negative electrodeactive material is caused to float on the surface of the electrode inthe pressing stage, resulting in failure to obtain a high densityelectrode having appropriate pores. It follows that the impregnationcapability of the negative electrode with the electrolyte is lowered. Inaddition, the battery performance is also lowered. On the other hand, ifthe roll temperature is higher than 180° C., the crystallizationproceeds in the binder to lower the flexibility of the electrode. Itfollows that the negative electrode porous layer tends to be folded orpeeled off. As a result, the productivity is lowered. In addition, thebattery performance such as the output characteristics and thecharge-discharge cycle characteristics is also lowered. It is moredesirable for the roll temperature to fall within a range of 90 to 150°C.

2) Nonaqueous Electrolyte

The nonaqueous electrolyte includes a liquid nonaqueous electrolyte thatis prepared by dissolving an electrolyte in an organic solvent and agel-like nonaqueous electrolyte that is prepared by using a compositematerial containing a liquid nonaqueous electrolyte and a polymermaterial.

Also, it is possible to permit the nonaqueous electrolyte to contain aroom temperature molten salt formed of a non-combustible ionic liquidthat is not volatile.

The liquid nonaqueous electrolyte can be prepared by dissolving anelectrolyte in an organic solvent in a concentration of 0.5 to 2.5mol/L.

The electrolyte includes, for example, lithium salts such as lithiumperchlorate (LiClO₄), lithium hexafluoro phosphate (LiPF₆), lithiumtetrafluoro borate (LiBF₄), lithium hexafluoro arsenate (LiAsF₆),lithium trifluoro metasulfonate (LiCF₃SO₃), bis-trifluoromethyl sulfonylimide lithium [LiN(CF₃SO₂)₂], and a mixture thereof. It is desirable touse an electrolyte that is unlikely to be oxidized under a highpotential. Particularly, it is most desirable to use LiPF₆ as theelectrolyte.

The organic solvent includes, for example, cyclic carbonates such aspropylene carbonate (PC), ethylene carbonate (EC) and vinylenecarbonate; linear carbonates such as diethyl carbonate (DEC), dimethylcarbonate (DMC) and methyl ethyl carbonate (MEC); cyclic ethers such astetrahydrofuran (THF), 2-methyl tetrahydrofuran (2Me THF) and dioxolane(DOX); linear ethers such as dimethoxy ethane (DME), and diethoxy ethane(DEE); as well as γ-butyrolactone (GBL), acetonitrile (AN) and sulfolane(SL). These solvents can be used singly or in the form of a mixedsolvent.

The polymer materials include, for example, polyvinylidene fluoride(PVdF), polyacrylonitrile (PAN) and polyethylene oxide (PEO).

It is desirable to use a mixed solvent prepared by mixing at least twoorganic solvents selected from the group consisting of propylenecarbonate (PC), ethylene carbonate (EC) and γ-butyrolactone (GBL). It ismore desirable to use γ-butyrolactone (GBL) as the organic solvent. Thereasons why these organic compounds can be used as excellent solventsare as follows.

First of all, each of γ-butyrolactone, propylene carbonate and ethylenecarbonate has a high boiling point and a high ignition point and isexcellent in the thermal stability.

Secondly, the titanium-containing metal composite oxide such as thelithium-titanium oxide absorbs and releases the lithium ions within thepotential region in the vicinity of 1.5V (vs. Li/Li⁺). However, it isimpossible to form sufficiently a film made of the reduction product ofthe nonaqueous electrolyte on the surface of the lithium-titanium oxideparticle within the potential region noted above, though it is certainlypossible to allow the nonaqueous electrolyte to be reduced anddecomposed within the potential region noted above. Therefore, if thebattery is stored under the charged state, the lithium ions absorbed inthe lithium-titanium composite oxide is gradually diffused into thenonaqueous electrolyte to bring about a so-called “self-discharge”. Theself-discharge is generated prominently if the battery is stored underan environment of a high temperature.

If the pore size and pore volume of the negative electrode arecontrolled as described in the first embodiment of the presentinvention, the contact area between the negative electrode and thenonaqueous electrolyte is increased, with the result that theself-discharge noted above tends to be somewhat increased.

It should be noted that γ-butyrolactone tends to be reduced easily,compared with the linear carbonate and the cyclic carbonate. To be morespecific, the solvents tend to be reduced in the order ofγ-butyrolactone>>>ethylene carbonate>propylene carbonate>>dimethylcarbonate>methyl ethyl carbonate>diethyl carbonate in the ordermentioned. Incidentally, the degree of difference in reactivity amongthe solvents is increased with increase in the number of signs ofinequality “>” noted above.

Such being the situation, if γ-butyrolactone is contained in thenonaqueous electrolyte, a satisfactory film is formed on the surface ofthe negative electrode even under the operating potential region of thelithium-titanium oxide. As a result, the self-discharge of the batteryis suppressed to improve the storage characteristics of the nonaqueouselectrolyte battery under high temperatures.

This is also the case with the mixed solvent noted above.

Also, a similar effect can be obtained in the case of using the ionicliquid that can be reduced easily. It should also be noted that theionic liquid also tends to be oxidized easily. Therefore, in the case ofusing the ionic liquid, the ionic liquid acts on the positive electrodeto produce the effect of suppressing the self-discharge and the effectof improving the charge-discharge cycle life.

In order to form a more satisfactory protective film, it is desirablefor the mixture of the organic solvents to contain 40 to 95% by volumeof γ-butyrolactone.

The nonaqueous electrolyte containing γ-butyrolactone, which exhibitsexcellent effects as described above, has a high viscosity to lower theimpregnation capability of the negative electrode with the nonaqueouselectrolyte. However, in the case of using the negative electrodespecified in the first embodiment of the present invention, the negativeelectrode is allowed to be impregnated smoothly with the nonaqueouselectrolyte even if the nonaqueous electrolyte contains γ-butyrolactoneto improve the productivity and to improve the output characteristicsand the charge-discharge cycle characteristics of the battery. It isalso possible to obtain a similar effect in the case of using the ionicliquid because of high viscosity. It follows that the negative electrodein the first embodiment of the present invention produces prominenteffects in the case of using the nonaqueous electrolyte containingγ-butyrolactone or an ionic liquid having a viscosity not lower than 5cp at 20° C.

It is possible to set the upper limit of the viscosity of the nonaqueouselectrolyte at 20° C. at 30 cp.

The nonaqueous electrolyte containing the ionic liquid will now bedescribed.

The ionic liquid denotes a salt which partly exhibits a liquid stateunder the room temperature. The term “room temperature” denotes thetemperature range within which the power source is assumed to beoperated in general. The upper limit of the temperature range withinwhich the power source is assumed to be operated in general is about120° C., or about 60° C. in some cases, and the lower limit is about−40° C. or about −20° C. in some cases. It is desirable for the roomtemperature to fall within a range of −20° C. to 60° C.

The ionic liquid should desirably contain lithium ions, organic cationsand organic anions. It is desirable for the ionic liquid to assume aliquid form even under the temperature not higher than room temperature.

The organic cation noted above includes, for example, quaternaryammonium ion and alkyl imidazolium ion having a skeleton represented bychemical formula (1) given below:

It is desirable to use dialkyl imidazolium ion, trialkyl imidazolium ionand tetraalkyl imidazolium ion as the alkyl imidazolium ion noted above.The dialkyl imidazolium ion includes, for example, 1-methyl-3-ethylimidazolium ion (MEI⁺). The trialkyl imidazolium ion includes, forexample, 1,2-diethyl-3-propyl imidazolium ion (DMPI⁺). And thetetraalkyl imidazolium ion includes 1,2-diethyl-3,4(5)-dimethylimidazolium ion.

On the other hand, the quaternary ammonium ion includes tetraalkylammonium ion and cyclic ammonium ion. The tetraalkyl ammonium ion notedabove includes dimethyl ethyl methoxy ammonium ion, dimethyl ethylmethoxy methyl ammonium ion, dimethyl ethyl ethoxy ethyl ammonium ion,and trimethyl propyl ammonium ion.

In the case of using the alkyl imidazolium ion or the quaternaryammonium ion (particularly, tetraalkyl ammonium ion) as the organiccation, it is possible to lower the melting point of the nonaqueouselectrolyte to 100° C. or less, more desirably to 20° C. or less.Further, it is possible to suppress the reactivity of the nonaqueouselectrolyte with the negative electrode.

It is desirable for the lithium ion concentration to be not higher than20 mol %, more desirably to fall within a range of 1 to 10 mol %. Wherethe lithium ion concentration falls within the range given above, theionic liquid can be formed easily even under the low temperature nothigher than 20° C. It is also possible to lower the viscosity of thenonaqueous electrolyte even under the temperature not higher than theroom temperature to increase the ionic conductivity.

The anion contained in the ionic liquid is selected from the groupconsisting of, for example, BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, ClO₄ ⁻, CF₃SO₃ ⁻,CF₃COO⁻, CH₃COO⁻, CO₃ ²⁻, N(CF₃SO₂)₂, N(C₂F₅SO₂)₂ ⁻, and (CF₃SO₂)₃C⁻. Itis desirable for the organic cation noted above to be present togetherwith at least one anion selected from the group given above. Where aplurality of anions are present together, an ionic liquid having amelting point not higher than 20° C. can be formed easily. Moredesirably, it is possible to obtain an ionic liquid having a meltingpoint not higher than 0° C. More desirable anions include, for example,BF₄ ⁻, CF₃SO₃ ⁻, CF₃COO⁻, CH₃COO⁻, CO₃ ²⁻, N(CF₃SO₂)₂ ⁻, N(C₂F₅SO₂)₂ ⁻,and (CF₃SO₂)₃C⁻. Where these anions are used, an ionic liquid having amelting point not higher than 0° C. can be formed easily.

3) Positive Electrode

The positive electrode includes a positive electrode current collectorand a positive electrode active material-containing layer supported onone surface or both surfaces of the positive electrode current collectorand containing a positive electrode active material, positive electrodeconductive agent and a binder.

The positive electrode active material includes, for example, an oxide,a sulfide and a polymer.

The oxides include, for example, manganese dioxide (MnO₂) absorbing Li,iron oxide, copper oxide, nickel oxide, a lithium-manganese compositeoxide (e.g., Li_(x)Mn₂O₄ or Li_(x)MnO₂), a lithium-nickel compositeoxide, e.g., Li_(x)NiO₂, a lithium-cobalt composite oxide (e.g.,Li_(x)CoO₂), a lithium-nickel-cobalt composite oxide, e.g.,LiNi_(1-y)Co_(y)O₂, a lithium-manganese-cobalt composite oxide (e.g.,LiMn_(y)Co_(1-y)O₂), a spinel type lithium-manganese-nickel compositeoxide (e.g., Li_(x)Mn_(2-y)Ni_(y)O₄), a lithium phosphorus oxide havingan olivine structure (e.g., Li_(x)FePO₄, Li_(x)Fe_(1-x)Mn_(y)PO₄,Li_(x)VPO₄F, and Li_(x)CoPO₄ (0≦x≦1, 0≦y≦1), iron sulfate (Fe₂(SO₄)₃),vanadium oxide (e.g., V₂O₅), and a lithium-nickel-cobalt-manganesecomposite oxide.

The polymer includes, for example, a conductive polymer material such aspolyaniline or polypyrrole, and a disulfide based polymer material. Itis also possible to use sulfur (S) and a fluorocarbon as the positiveelectrode active material.

The positive electrode active material that permits obtaining a highpositive electrode voltage includes, for example, a lithium-manganesecomposite oxide (Li_(x)Mn₂O₄), a lithium-nickel composite oxide(Li_(x)NiO₂), a lithium-cobalt composite oxide (Li_(x)CoO₂), alithium-nickel-cobalt composite oxide (Li_(x)Ni_(1-y)Co_(y)O₂), a spineltype lithium-manganese-nickel composite oxide (Li_(x)Mn_(2-y)Ni_(y)O₄),a lithium-manganese-cobalt composite oxide (li_(x)Mn_(y)Co_(1-y)O₂), alithium phosphorus oxide (Li_(x)FePO₄), and alithium-nickel-cobalt-manganese composite oxide. Incidentally, it isdesirable for each of the molar ratios x and y to fall within a range of0<x≦1, 0<y≦1.

It is desirable for the lithium-nickel-cobalt-manganese composite oxideto have a composition of Li_(a)Ni_(b)Co_(c)Mn_(d)O₂ (where the molarratios a, b, c and d are: 0≦a≦1.1, 0.1≦b≦0.5, 0≦c≦0.9, 0.1≦d≦0.5).

Particularly, in the case of using a nonaqueous electrolyte containingan ionic liquid, it is desirable in view of the charge-discharge cyclelife of the battery to use the positive electrode active materialselected from the group consisting of the lithium iron phosphate,Li_(x)VPO₄F, a lithium-manganese composite oxide, a lithium-nickelcomposite oxide, and a lithium-nickel-cobalt composite oxide. Since thereactivity between the positive electrode active material exemplifiedabove and the ionic liquid is low, it is possible to obtain a longcharge-discharge cycle life of the battery as pointed out above.

Also, the positive electrode active material for the primary batteryincludes, for example, manganese dioxide, iron oxide, copper oxide, ironsulfide and a fluorocarbon.

It is desirable for the diameters of the primary particles of thepositive electrode active material to fall within a range of 100 nm to 1μm. If the diameter of the primary particle is not smaller than 100 nm,the primary particles can be handled easily in the industrialmanufacture of the positive electrode. Also, if the primary particles ofthe positive electrode active material is not larger than 1 μm, thelithium ions can be diffused smoothly within the positive electrodeactive material.

It is desirable for the specific surface area of the positive electrodeactive material to fall within a range of 0.1 m²/g to 10 m²/g. If thespecific surface area of the positive electrode active material is notsmaller than 0.1 m²/g, it is possible to secure sufficiently theabsorption-release sites of the lithium ions. On the other hand, if thespecific surface area of the positive electrode active material is notlarger than 10 m²/g, the positive electrode active material can behandled easily in the industrial manufacture of the positive electrode.Also, it is possible to secure a good charge-discharge cycle performanceof the battery.

The positive electrode conductive agent permits enhancing the currentcollecting performance and also permits suppressing the contactresistance between the current collector and the active material. Thepositive electrode conductive agent includes, for example, acarbonaceous material such as acetylene black, carbon black andgraphite.

The binder for bonding the positive electrode active material to thepositive electrode conductive agent includes, for example,polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) and afluorinated rubber.

Concerning the mixing ratio of the positive electrode active material,the positive electrode conductive agent, and the binder, it is desirablefor the mixing amount of the positive electrode active material to benot smaller than 80% by weight and not larger than 95% by weight, forthe mixing amount of the positive electrode conductive agent to be notsmaller than 3% by weight and not larger than 18% by weight, and for themixing amount of the binder to be not smaller than 2% by weight and notlarger than 17% by weight. If the positive electrode conductive agent ismixed in an amount not smaller than 3% by weight, it is possible toobtain the effects described above. On the other hand, if the mixingamount of the positive electrode conductive agent is not larger than 18%by weight, it is possible to suppress the decomposition of thenonaqueous electrolyte on the surface of the positive electrodeconductive agent during storage of the nonaqueous electrolyte batteryunder high temperatures. Further, where the binder is used in an amountnot smaller than 2% by weight, it is possible to obtain a sufficientelectrode strength. On the other hand, where the mixing amount of thebinder is not larger than 17% by weight, it is possible to decrease themixing amount of the insulator in the electrode to decrease the internalresistance of the nonaqueous electrolyte battery.

The positive electrode can be prepared by, for example, suspending thepositive electrode active material, the conductive agent and the binderin an appropriate solvent, followed by coating a current collector withthe resultant suspension and subsequently drying and pressing thecurrent collector coated with the suspension. It is also possible toform a mixture of a positive electrode active material, a positiveelectrode conductive agent and a binder into the shape of pellets. Inthis case, the pellets thus formed is used for forming the positiveelectrode layer.

It is desirable for the positive electrode current collector to beformed of an aluminum foil or an aluminum alloy foil. It is desirablefor the aluminum foil or the aluminum alloy foil forming the positiveelectrode current collector to have an average crystal grain size notlarger than 50 μm. It is more desirable for the average crystal grainsize noted above to be not larger than 30 μm, and furthermore desirablynot larger than 5 μm. Where the average crystal grain size of thealuminum foil or the aluminum alloy foil forming the positive electrodecurrent collector is not larger than 50 μm, the mechanical strength ofthe aluminum foil or the aluminum alloy foil can be drasticallyincreased to make it possible to press the positive electrode with ahigh pressure. It follows that the density of the positive electrode canbe increased to increase the battery capacity.

The aluminum foil or the aluminum alloy foil having the average crystalgrain size not larger than 50 μm can be affected in a complicatedfashion by many factors such as the composition of the material, theimpurities, the process conditions, the history of the heat treatmentsand the heating conditions such as the annealing conditions, and thecrystal grain size can be adjusted by an appropriate combination of thefactors noted above during the manufacturing process.

It is desirable for the aluminum foil or the aluminum alloy foil to havea thickness not larger than 20 μm, preferably not larger than 15 μm.Also, it is desirable for the aluminum foil to have a purity not lowerthan 99%. Further, it is desirable for the aluminum alloy to contain,for example, magnesium, zinc and silicon. On the other hand, it isdesirable for the content of the transition metals such as iron, copper,nickel and chromium in the aluminum alloy to be not higher than 1%.

4) Separator

The separator includes, for example, a porous film includingpolyethylene, polypropylene, cellulose and/or polyvinylidene fluoride(PVdF), and an unwoven fabric made of a synthetic resin. Particularly,it is desirable in view of the improvement in safety to use a porousfilm made of polyethylene or polypropylene because the particular porousfilm can be melted under a prescribed temperature to break the current.

5) Case

The case is formed of a laminate film having a thickness of, forexample, 0.2 mm or less, or a metal sheet having a thickness of, forexample, 0.5 mm or less. It is more desirable for the metal sheet tohave a thickness of 0.2 mm or less. Also, the case has a flattenedshape, an angular shape, a cylindrical shape, a coin shape, a buttonshape or a sheet shape, or is of a laminate type. The case includes acase of a large battery mounted to, for example, an electric automobilehaving two to four wheels in addition to a small battery mounted to aportable electronic device.

The laminate film includes, for example, a multi-layered film includinga metal layer and a resin layer covering the metal layer. For decreasingthe weight of the battery, it is desirable for the metal layer to beformed of an aluminum foil or an aluminum alloy foil. On the other hand,the resin layer for reinforcing the metal layer is formed of a polymermaterial such as polypropylene (PP), polyethylene (PE), Nylon, andpolyethylene terephthalate (PET). The laminate film case can be obtainedby bonding the periphery of superposed laminate films by the thermalfusion.

It is desirable for the metal case to be formed of aluminum or analuminum alloy. Also, it is desirable for the aluminum alloy to be analloy containing an element such as magnesium, zinc or silicon. On theother hand, it is desirable for the amount of the transition metals,which are contained in the aluminum alloy, such as iron, copper, nickeland chromium, to be not larger than 1%. In this case, it is possible toimprove the battery in respect of reliability for a long time in ahigh-temperature environment, and heat dissipating properties.

It is desirable for the metal can formed of aluminum or an aluminumalloy to have an average crystal grain size not larger than 50 μm, morepreferably not larger than 30 μm, and furthermore preferably not largerthan 5 μm. Where the average crystal grain size is not larger than 50μm, it is possible to increase drastically the mechanical strength ofthe metal can formed of aluminum or an aluminum alloy to make itpossible to decrease the thickness of the metal can used as the case. Asa result, it is possible to realize a battery that is light in weight,high in output, excellent in reliability over a long period, and adaptedfor mounting on a vehicle.

6) Negative Electrode Terminal

The negative electrode terminal is formed of a material exhibiting anelectrical stability and conductivity within the range of 0.4V to 3V ofthe potential relative to the lithium metal. To be more specific, thematerial used for forming the negative electrode terminal includes, forexample, aluminum and an aluminum alloy containing at least one elementselected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu and Si. Inorder to lower the contact resistance relative to the negative electrodecurrent collector, it is desirable for the negative electrode terminalto be formed of a material equal to the material used for forming thenegative electrode current collector.

7) Positive Electrode Terminal

The positive electrode terminal is formed of a material exhibiting anelectrical stability and conductivity within the range of 3V to 5V ofthe potential relative to the lithium ion metal. To be more specific,the material used for forming the positive electrode terminal includes,for example, aluminum and an aluminum alloy containing at least oneelement selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu andSi. In order to lower the contact resistance relative to the positiveelectrode current collector, it is desirable for the positive electrodeterminal to be formed of a material equal to the material used forforming the positive electrode current collector.

The construction of the nonaqueous electrolyte battery according to thefirst embodiment of the present invention is not limited to that shownin FIGS. 1 and 2. It is possible for the nonaqueous electrolyte batteryaccording to the first embodiment of the present invention to beconstructed as shown in FIGS. 3 and 4. Specifically, FIG. 3 is a crosssectional view, partly broken away, schematically showing theconstruction of another flat type nonaqueous electrolyte batteryaccording to the first embodiment of the present invention, and FIG. 4is a cross sectional view showing in a magnified fashion theconstruction of the circular region B shown in FIG. 3.

As shown in FIG. 3, a laminate type electrode group 9 is housed in acase 8 made of a laminate film. Two short sides and one long side of thecase 8 are sealed by the heat seal. The sealed section formed in one ofthe short sides is called a first sealed section 8 a. The sealed sectionformed in the short side opposite to the first sealed section 8 a iscalled a second sealed section 8 b. Further, the sealed section formedon the long side is called a third sealed section 8 c. As shown in FIG.4, the laminate type electrode group 9 is constructed such that apositive electrode 3 and a negative electrode 4 are laminated one uponthe other with a separator 5 interposed between the positive electrode 3and the negative electrode 4. A plurality of positive electrodes 3 arehoused in the case 8. Each of these positive electrodes 3 comprises apositive electrode current collector 3 a and positive electrode activematerial-containing layers 3 b supported on both surfaces of thepositive electrode current collector 3 a. Likewise, a plurality ofnegative electrodes 4 are housed in the case 8. Each of these negativeelectrodes 4 comprises a negative electrode current collector 4 a andnegative electrode active material-containing layers 4 b formed on bothsurfaces of the negative electrode current collector 4 a. The negativeelectrode active material-containing layers 4 b is porous. The negativeelectrode current collector 4 a included in each negative electrode 4protrudes at one side from the positive electrode 3. The negativeelectrode current collector 4 a protruding from the positive electrode 3is electrically connected to a band-like negative electrode terminal 2.The tip portion of the band-like negative electrode terminal 2 iswithdrawn to the outside from the second sealed section 8 b of the case8. The positive electrode current collector 3 a of the positiveelectrode 3 protrudes from the negative electrode 4 at the sidepositioned opposite to the protruding side of the negative electrodecurrent collector 4 a, though the protruding side of the positiveelectrode current collector 3 a is not shown in the drawing. Thepositive electrode current collector 3 a protruding from the negativeelectrode 4 is electrically connected to a band-like positive electrodeterminal 1. The tip portion of the band-like positive electrode terminal1 is positioned on the opposite side of the negative electrode terminal2 and is withdrawn to the outside from the first sealed section 8 a ofthe case 8.

Second Embodiment

A battery pack according to a second embodiment of the present inventioncomprises a plurality of unit cells each consisting of the nonaqueouselectrolyte battery according to the first embodiment of the presentinvention. The plural unit cells are connected to each other in seriesor in parallel to form a battery module.

The unit cell (nonaqueous electrolyte battery) according to the firstembodiment of the present invention is adapted for preparation of thebattery module, and the battery pack according to the second embodimentof the present invention is excellent in the charge-discharge cyclecharacteristics, as described in the following.

If the impregnation capability of the negative electrode with thenonaqueous electrolyte is improved, it is possible to bring the entiresurface of the negative electrode active material into contact with thenonaqueous electrolyte. As a result, the lithium ion concentrationwithin the negative electrode active material tends to be made uniformeasily, and, thus, an over-voltage is unlikely to be applied, i.e., alocal over-charging and over-discharge is unlikely to be brought aboutto make uniform the utilization rate of the negative electrode activematerial. It follows that the differences in the battery capacity and inthe impedance among the individual batteries can be made very small. Asa result, it is possible to decrease the unevenness in the batteryvoltage derived from the difference in the battery capacity among theindividual batteries in the battery module consisting of a plurality ofbatteries that are connected in series when the battery module ischarged full. It follows that the battery pack according to the secondembodiment of the present invention is excellent in the controllabilityof the battery module voltage, and the charge-discharge cyclecharacteristics of the battery pack can be improved.

It is possible to use the flat type battery shown in FIG. 1 or FIG. 3 asthe unit cell included in the battery module.

Each of a plurality of unit cells 21 included in the battery pack shownin FIG. 5 is formed of a flattened type nonaqueous electrolyte batteryconstructed as shown in FIG. 1. The plural unit cells 21 are stacked oneupon the other in the thickness direction in a manner to align theprotruding directions of the positive electrode terminals and thenegative electrode terminals. As shown in FIG. 6, the unit cells 21 areconnected in series to form a battery module 22. The unit cells 21forming the battery module 22 are made integral by using an adhesivetape 23 as shown in FIG. 5.

A printed wiring board 24 is arranged on the side surface of the batterymodule 22 toward which protrude the positive electrode terminals 1 andthe negative electrode terminals 2. As shown in FIG. 6, a thermistor 25,a protective circuit 26 and a terminal 27 for current supply to theexternal equipment are connected to the printed wiring board 24.

As shown in FIGS. 5 and 6, a wiring 28 on the side of the positiveelectrodes of the battery module 22 is electrically connected to aconnector 29 on the side of the positive electrode of the protectivecircuit 26 mounted to the printed wiring board 24. On the other hand, awiring 30 on the side of the negative electrodes of the battery module22 is electrically connected to a connector 31 on the side of thenegative electrode of the protective circuit 26 mounted to the printedwiring board 24.

The thermistor 25 detects the temperature of the unit cell 21 andtransmits the detection signal to the protective circuit 26. Theprotective circuit 26 is capable of breaking a wiring 31 a on thepositive side and a wiring 31 b on the negative side, the wirings 31 aand 31 b being stretched between the protective circuit 26 and theterminal 27 for current supply to the external equipment. These wirings31 a and 31 b are broken by the protective circuit 26 under prescribedconditions including, for example, the conditions that the temperaturedetected by the thermistor is higher than a prescribed temperature, andthat the over-charging, over-discharging and over-current of the unitcell 21 have been detected. The detecting method is applied to the unitcells 21 or to the battery module 22. In the case of applying thedetecting method to each of the unit cells 21, it is possible to detectthe battery voltage, the positive electrode potential or the negativeelectrode potential. On the other hand, where the positive electrodepotential or the negative electrode potential is detected, lithiumelectrodes used as reference electrodes are inserted into the unit cells21.

In the case of FIG. 6, a wiring 32 is connected to each of the unitcells 21 for detecting the voltage, and the detection signal istransmitted through these wirings 32 to the protective circuit 26.Specifically, the protective circuit 26 is provided with a batteryvoltage monitoring circuit section. Each of the unit cells 21 isconnected to the battery voltage monitoring circuit section via a wiring32. According to the particular construction, the battery voltage ofeach of the unit cells 21 can be detected by the protective circuit 26.

Further, in the case shown in FIG. 6, all the unit cells 21 included inthe battery module 22 are detected in terms of voltage. Although it isparticularly preferable that the voltages of all of the unit cells 21 ofthe battery module 22 should be detected, it may be sufficient to checkthe voltages of only some of the unit cells 21.

Protective sheets 33 each formed of rubber or resin are arranged on thethree of the four sides of the battery module 22, though the protectivesheet 33 is not arranged on the side toward which protrude the positiveelectrode terminals 1 and the negative electrode terminals 2. Aprotective block 34 formed of rubber or resin is arranged in theclearance between the side surface of the battery module 22 and theprinted wiring board 24.

The battery module 22 is housed in a container 35 together with each ofthe protective sheets 33, the protective block 34 and the printed wiringboard 24. To be more specific, the protective sheets 33 are arrangedinside the two long sides of the container 35 and inside one short sideof the container 35. On the other hand, the printed wiring board 24 isarranged along that short side of the container 35 which is opposite tothe short side along which one of the protective sheets 33 is arranged.The battery module 22 is positioned within the space surrounded by thethree protective sheets 33 and the printed wiring board 24. Further, alid 36 is mounted to close the upper open edge of the container 35.

Incidentally, it is possible to use a thermally shrinkable tube in placeof the adhesive tape 23 for fixing the battery module 22. In this case,the protective sheets 33 are arranged on both sides of the batterymodule 22 and, after the thermally shrinkable tube is wound about theprotective sheets, the tube is thermally shrunk to fix the batterymodule 22.

The unit cells 21 shown in FIGS. 5 and 6 are connected in series.However, it is also possible to connect the unit cells 21 in parallel toincrease the cell capacity. Of course, it is possible to connect thebattery packs in series and in parallel.

Also, the construction of the battery pack can be changed appropriatelydepending on the use of the battery pack.

It is desirable for the battery pack according to the second embodimentof the present invention to be used in the field requiring high ratecharge-discharge cycle characteristics. To be more specific, it isdesirable for the battery pack according to the second embodiment of thepresent invention to be used in, for example, a digital camera as apower supply, or mounted in a vehicle such as a hybrid electricautomobile having two to four wheels, an electric automobile having twoto four wheels, and or a power-assisted bicycle. Particularly, it isdesirable for the battery back of the present invention to be mounted toa vehicle.

Where the nonaqueous electrolyte contains a mixed solvent containing atleast two kinds of the compounds selected from the group consisting ofpropylene carbonate (PC), ethylene carbonate (EC) and γ-butyrolactone(GBL), or where the solvent of the nonaqueous electrolyte containsγ-butyrolactone (GBL), it is desirable for the battery pack of thesecond embodiment to be used in a field requiring good high temperaturecharacteristics, particularly, to be used in the types of vehicle notedabove.

Described in the following are Examples of the present invention.Needless to say, the technical scope of the present invention is notlimited to the following Examples, as far as the subject matter of thepresent invention is not exceeded.

Example 1 Preparation of Positive Electrode

In the first step, a slurry was prepared by adding 90% by weight of alithium-nickel-cobalt-manganese composite oxide(LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂) powder used as a positive electrodeactive material, 5% by weight of acetylene black used as a conductiveagent, and 5% by weight of polyvinylidene fluoride (PVdF) to N-methylpyrrolidone (NMP). Both surfaces of a current collector formed of analuminum foil having a thickness of 15 μm were coated with the slurrythus prepared, followed by drying and, then, pressing the currentcollector coated with the slurry to obtain a positive electrode havingan electrode density of 3.3 g/cm³.

<Preparation of Negative Electrode>

Prepared as a negative electrode active material was a lithium titanatepowder represented by Li₄Ti₅O₁₂, and having a spinel structure, anaverage particle diameter of 0.82 μm, the BET specific surface area,utilizing N₂ adsorption, of 10.4 m²/g and 1.55V (vs. Li/Li⁺) of the Liion insertion potential.

The measuring methods of the particle diameter and the lithium ioninsertion potential of the negative electrode active material will nowbe described.

<Particle Diameter>

Specifically, about 0.1 g of a sample, a surfactant, and 1 to 2 mL of adistilled water were put in a beaker, and the distilled water wassufficiently stirred, followed by pouring the stirred system in astirring water vessel. Under this condition, the light intensitydistribution was measured every 2 seconds and measured 64 times in totalby using SALD-300, which is a Laser Diffraction Particle Size Analyzermanufactured by Shimadzu Corporation, to analyze the particle diameterdistribution data.

<Lithium Ion Insertion Potential>

The negative electrode was cut into small pieces each sized at 2 cm×2 cmto obtain working electrodes. The working electrode was disposed to facea counter electrode formed of a lithium metal foil sized at 2.2 cm×2.2cm with a glass filter (separator) interposed therebetween, and alithium metal used as a reference electrode was inserted so as not to bebrought into contact with any of the working electrode and the counterelectrode. These electrodes were put in a glass cell of a three poletype such that each of the working electrode, the counter electrode andthe reference electrode was connected to the terminal of the glass cell.Under the particular condition, 25 mL of an electrolysis solution, whichwas prepared by dissolving LiBF₄ in a concentration of 1.5 mol/L in amixed solvent prepared by mixing ethylene carbonate (EC) andγ-butyrolactone (GBL) in a mixing ratio by volume of 1:2, was pouredinto the glass cell such that the separator and the electrodes weresufficiently impregnated with the electrolysis solution, followed byhermetically closing the glass cell. The glass cell thus manufacturedwas arranged in a constant temperature bath maintained at 25V to measurethe lithium ion insertion potential of the working electrode at the timewhen the glass cell was charged with a current density of 0.1 mA/cm².Incidentally, a constant temperature bath type No. EC-45 MTPmanufactured by Hitachi Ltd. was used as the constant temperature bath.

Prepared was a slurry by adding N-methyl pyrrolidone (NMP) to a mixtureconsisting of 90% by weight of the negative electrode active material,5% by weight of coke used as a conductive agent and baked at 1,300° C.,which has a lattice spacing d₀₀₂ of 0.3465 nm, an average particlediameter of 8.2 μm, and the BET specific surface area of 11.2 m²/g, and5% by weight of polyvinylidene fluoride (PVdF) such that the resultantslurry had a solid component ratio of 62%. The slurry thus prepared waskneaded by using a planetary mixer while adding NMP to the slurry tolower gradually the solid component ratio of the slurry, therebyobtaining a slurry having a viscosity of 10.2 cp, which was obtained bythe measurement with a B-type viscometer under the condition of 50 rpm.The slurry thus obtained was further mixed by using a bead mill in whichzirconia balls each having a diameter of 1 mm were used as the mixingmedium.

Both surfaces of a current collector formed of an aluminum foil having apurity of 99.99% and an average crystal grain size of 10 μm, and alsohaving a thickness of 15 μm were coated with the slurry thus obtained,followed by drying the aluminum foil coated with the slurry and, then,subjecting the aluminum foil coated with the slurry to a roll pressingby using a roll heated to 100° C. to obtain a negative electrode havingan electrode density and a porosity shown in Table 1. The pore diameterdistribution of the negative electrode thus obtained was measured by themercury porosimetry by the method described in the following. The resultof the measurement is shown in Table 4.

The pore diameter distribution of the negative electrode was measured bythe mercury porosimetry. Shimadzu Auto pore type 9520 was used as themeasuring apparatus. Samples were prepared by cutting the negativeelectrode into small pieces each sized at about 25×25 mm², and thesamples thus prepared were folded and put in a measuring cell, and thepore diameter distribution of the negative electrode was measured underthe condition of the initial pressure of 20 kPa (about 3 psia,corresponding to the pore diameter of about 60 μm). In the data, thespecific surface area of the pores was calculated under the assumptionthat the pore was shaped cylindrical. The diameter of the pore havingthe highest frequency in the pore diameter distribution was regarded asthe mode diameter of the negative electrode. The pore diameter havingthe highest frequency within the pore diameter range of 0.01 to 0.2 μmwas regarded as the mode diameter of the first peak. On the other hand,the pore diameter having the highest frequency within the pore diameterrange of 0.003 to 0.02 μm was regarded as the mode diameter of thesecond peak.

Incidentally, the analytical principle of the mercury porosimetry isbased on Washburn's formula (1) given below:

D=−4γ cos θ/P  (1)

where P denotes the applied pressure, D denotes the diameter of thepore, γ denotes the surface tension of mercury (480 dyne·cm⁻¹), and θdenotes the contact angle between mercury and the wall of the pore,which was 140°. Since γ and θ are constants, it is possible to obtainthe relationship between the applied pressure P and the pore diameter Dfrom Washburn's formula (1) given above, and the pore diameter and thepore volume distribution can be obtained by measuring the volume of themercury entering the pores. The details of the measuring method, theprinciple, etc. are described in, for example, “Biryushi Handbook (FineParticle Handbook)” by Motoji Jinpo et al., published by Asakura shotenK.K. in 1991 and “Huntaibussei Sokuteihou (Method of MeasuringProperties of Powdery Material)” by Sohachiro Hayakawa, published byAsakura shoten K.K. in 1978.

Table 4 shows the pore volume per gram of the negative electrodeexcluding the negative electrode current collector (entire range of thepore diameter distribution, within pore diameter range of 0.01 to 0.2 μmand within pore diameter range of 0.003 to 0.02 μm), the surface area ofthe pores in the negative electrode per gram of the negative electrodeexcluding the negative electrode current collector (entire range of thepore diameter distribution, within pore diameter range of 0.01 to 0.2 μmand within pore diameter range of 0.003 to 0.02 μm), the mode diametersof the first peak and the second peak, and the mode diameter of thenegative electrode.

<Preparation of Electrode Group>

A positive electrode, a separator formed of a porous polyethylene filmhaving a thickness of 25 μm, a negative electrode, and another separatorequal to that noted above were alternately laminated one upon the otherin the order mentioned to obtain a laminate structure, followed byspirally winding the laminate structure thus obtained. Then, thespirally wound laminate structure was subjected to a hot press at 90° C.to obtain an electrode group having a width of 30 mm and a thickness of3.0 mm. The electrode group thus obtained was housed in a pack formed ofa laminate film having a thickness of 0.1 mm and comprising an aluminumfoil having a thickness of 40 μm, and polypropylene layers formed onboth sides of the aluminum foil, and the electrode group housed in thepack of the laminate film was subjected to a vacuum drying at 80° C. for24 hours.

<Preparation of Liquid Nonaqueous Electrolyte>

A liquid nonaqueous electrolyte was prepared by dissolving LiBF₄ used asan electrolyte in an amount of 1.5 mol/L in a mixed solvent prepared bymixing ethylene carbonate (EC) and γ-butyrolactone (GBL) in a volumeratio of 1:2. The viscosity at 20° C. of the liquid nonaqueouselectrolyte thus prepared was found to be 7.1 cp as measured by theB-type viscometer.

After the liquid nonaqueous electrolyte was poured into the laminatefilm pack housing the electrode group, the pack was perfectly sealed bya heat seal to obtain a nonaqueous electrolyte secondary batteryconstructed as shown in FIG. 1 and having a width of 35 mm, a thicknessof 3.2 mm and a height of 65 mm.

Examples 2 to 13 and Comparative Example 1

A negative electrode was prepared as in Example 1, except that thediameter of the ball used in the slurry stirring stage and the stirringtime were changed as shown in Table 1. Table 1 shows the negativeelectrode density and the porosity of the negative electrode, and Table4 shows the pore diameter distribution in the negative electrode. Then,a nonaqueous electrolyte secondary battery was manufactured as inExample 1, except that used was the negative electrode thus obtained andthe nonaqueous electrolyte having a composition shown in Table 1.

Example 14

A nonaqueous electrolyte secondary battery was manufactured as inExample 13, except that the nonaqueous electrolyte used was formed of anionic liquid (MEI/Li/BF₄) prepared by mixing 1-methyl-3-ethylimidazolium ion (MEI⁺), Li⁺ and BF₄ ⁻ in a molar ratio of 40:10:50. Theviscosity of the nonaqueous electrolyte at 20° C. was found to be 20 cp.

Example 15

A nonaqueous electrolyte secondary battery was manufactured as inExample 14, except that dimethyl ethyl methoxy methyl ammonium ion(hereinafter referred to as ammonium ion) was used in place of1-methyl-3-ethyl imidazolium ion (MEI⁺). The viscosity of the nonaqueouselectrolyte at 20° C. was found to be 20 cp.

Example 16

A nonaqueous electrolyte secondary battery was manufactured as inExample 13, except that lithium-cobalt oxide (LiCoO₂) was used as thepositive electrode active material.

Example 17

A nonaqueous electrolyte secondary battery was manufactured as inExample 13, except that lithium iron phosphate (LiFePO₄) was used as thepositive electrode active material.

Example 18

A liquid nonaqueous electrolyte was prepared by dissolving LiPF₆ used asan electrolyte in an amount of 1 mol/L in a mixed solvent prepared bymixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volumeratio of 1:2. The viscosity at 20° C. of the liquid nonaqueouselectrolyte thus prepared was found to be 1.9 cp. Then, a nonaqueouselectrolyte secondary battery was manufactured as in Example 13, exceptthat used was the liquid nonaqueous electrolyte thus prepared.

Examples 19 and 20

A negative electrode was prepared as in Example 1, except that used asthe negative electrode active material was a lithium titanate powderrepresented by the chemical formula of Li₄Ti₅O₁₂, having a spinelstructure, and also having the average particle diameter and the BETspecific surface area utilizing the N₂ absorption, which are shown inTable 2, and having a Li ion insertion potential of 1.55V (vs. Li/Li⁺).Table 2 shows the density and the porosity of the negative electrodethus obtained, and Table 5 shows the pore diameter distribution in thenegative electrode thus prepared. Then, a nonaqueous electrolytesecondary battery was manufactured as in Example 1, except that used wasthe negative electrode thus prepared.

Comparative Example 2

A negative electrode was prepared as in Example 1, except that used asthe negative electrode active material was a lithium titanate powderrepresented by the chemical formula of Li₄Ti₅O₁₂, having a spinelstructure, having the average particle diameter and the BET specificsurface area utilizing the N₂ absorption, which are shown in Table 2,and also having a Li ion insertion potential of 1.55V (vs. Li/Li⁺).Table 2 shows the density and the porosity of the negative electrodethus obtained, and Table 5 shows the pore diameter distribution in thenegative electrode thus prepared. Then, a nonaqueous electrolytesecondary battery was manufactured as in Example 1, except that used wasthe negative electrode thus prepared.

Example 21

A negative electrode was prepared as in Example 1, except that used asthe negative electrode active material was an FeS powder having theaverage particle diameter and the BET specific surface area utilizingthe N₂ absorption, which are shown in Table 2, and having a Li ioninsertion potential of 1.8V (vs. Li/Li⁺). Table 2 shows the density andthe porosity of the negative electrode thus obtained, and Table 5 showsthe pore diameter distribution in the negative electrode thus prepared.Then, a nonaqueous electrolyte secondary battery was manufactured as inExample 1, except that used was the negative electrode thus prepared.

Example 22

A negative electrode was prepared as in Example 1, except that used asthe negative electrode active material was a lithium titanate powderrepresented by the chemical formula of Li₂Ti₃O₇, having the averageparticle diameter and the BET specific surface area utilizing the N₂absorption, which are shown in Table 2, and having a Li ion insertionpotential of 1 to 2V (vs. Li/Li⁺). Table 2 shows the density and theporosity of the negative electrode thus obtained, and Table 5 shows thepore diameter distribution in the negative electrode thus prepared.Then, a nonaqueous electrolyte secondary battery was manufactured as inExample 1, except that used was the negative electrode thus prepared.

Examples 23 and 24

A negative electrode was prepared as in Example 1, except that used asthe negative electrode active material was a titanium-containing metalcomposite oxide containing a microcrystalline phase of TiO₂ and anon-crystalline phase (an amorphous phase) of TiO₂. Thetitanium-containing metal composite oxide was represented byTiO₂—P₂O₅—SnO₂—NiO—CuO, had the average particle diameter and the BETspecific surface area utilizing the N₂ absorption, which are shown inTable 2, and also had a Li ion insertion potential of 1 to 2V (vs.Li/Li⁺). Table 2 shows the density and the porosity of the negativeelectrode thus obtained, and Table 5 shows the pore diameterdistribution in the negative electrode thus prepared. Then, a nonaqueouselectrolyte secondary battery was manufactured as in Example 1, exceptthat used was the negative electrode thus prepared.

Comparative Example 3

Prepared as the negative electrode active material was atitanium-containing metal composite oxide containing a microcrystallinephase of TiO₂ and a non-crystalline phase. The titanium-containing metalcomposite oxide was represented by TiO₂—P₂O₅—SnO₂—NiO—CuO, had theaverage particle diameter and the BET specific surface area utilizingthe N₂ absorption, which are shown in Table 2, and also had a Li ioninsertion potential of 1 to 2V (vs. Li/Li⁺).

The total amount of N-methylpyrrolidone (NMP) was added to a mixtureconsisting of 90% by weight of the negative electrode active materialnoted above, 5% by weight of the conductive agent equal to that used inExample 1 and 5% by weight of polyvinylidene fluoride (PVdF). Theresultant mixture was kneaded by using a planetary mixer to prepare aslurry. Then, both surfaces of a current collector similar to that usedin Example 1 were coated with the slurry thus obtained, followed bydrying and, then, subjecting the current collector coated with theslurry to a roll press to obtain a negative electrode. Table 2 shows thedensity and the porosity of the negative electrode thus prepared, andTable 5 shows the pore diameter distribution in the negative electrode.A nonaqueous electrolyte secondary battery was manufactured as inExample 1, except that used was the negative electrode thus obtained.

Comparative Example 4

Prepared as the negative electrode active material was a graphite havingthe average particle diameter and the BET specific surface area,determined by N₂ adsorption, as shown in Table 2, and also having a Liion insertion potential of 0.15V (vs. Li/Li⁺).

The total amount of N-methylpyrrolidone (NMP) was added to a mixtureconsisting of 90% by weight of the negative electrode active materialnoted above, 5% by weight of the conductive agent equal to that used inExample 1 and 5% by weight of polyvinylidene fluoride (PVdF). Theresultant mixture was kneaded by using a planetary mixer to prepare aslurry. Then, both surfaces of a current collector formed of a copperfoil having a thickness of 12 μm were coated with the slurry thusobtained, followed by drying and, then, subjecting the current collectorcoated with the slurry to a roll press to obtain a negative electrode.Table 2 shows the density and the porosity of the negative electrodethus prepared, and Table 5 shows the pore diameter distribution in thenegative electrode. Then, a nonaqueous electrolyte secondary battery wasmanufactured as in Example 1, except that used was the negativeelectrode thus obtained.

Examples 25 to 31

A negative electrode was prepared as in Example 1, except that thediameter of the ball used in the stirring stage for preparing the slurryand the stirring time were changed as shown in Table 3. Table 3 alsoshows the density and the porosity of the negative electrode, and Table6 shows the pore diameter distribution in the negative electrode. Then,a nonaqueous electrolyte secondary battery was manufactured as inExample 1, except that used was the negative electrode thus prepared.

Comparative Example 5

Prepared as a negative electrode active material was graphite having anaverage particle diameter and a BET specific surface area, determined byN₂ adsorption, as shown in Table 3, and also having a Li ion insertionpotential of 0.15V (vs. Li/Li⁺). Then, a negative electrode wasmanufactured as in Example 1, except that the graphite thus prepared wasused as the negative electrode active material, and that a copper foilhaving a thickness of 12 μm was used as a current collector. Table 3shows the density and the porosity of the negative electrode thusmanufactured, and Table 6 shows the pore diameter distribution in thenegative electrode. Further, a nonaqueous electrolyte secondary batterywas manufactured as in Example 1, except that used was the negativeelectrode thus obtained.

The nonaqueous electrolyte secondary battery manufactured in each of theExamples and the Comparative Examples excluding Comparative Examples 4and 5 was charged for one hour under an environment of 25° C. and undera constant voltage of 2.8V, followed by discharging the nonaqueouselectrolyte secondary battery under a low current of 0.2 A to measurethe discharge capacity of 0.2 A. Also, after charged under the sameconditions, the nonaqueous electrolyte secondary battery was dischargedunder a high current of 2 A to measure the discharge capacity of 2 A. Aratio of the 2 A discharge capacity to the 0.2 A discharge capacity wasobtained from the experimental data thus obtained. Further, acharge-discharge cycle test was conducted by repeatedlycharging-discharging the nonaqueous electrolyte secondary battery suchthat the secondary battery was charged under the conditions given above,followed by discharging the secondary battery under a current of 600 mAuntil the battery voltage was lowered to 1.5V. The number ofcharge-discharge cycles that were performed before the battery capacitywas lowered to 800 of the initial capacity was measured to determine thecharge-discharge cycle life. Tables 4 to 6 show the experimental data.

The nonaqueous electrolyte secondary battery manufactured in each ofComparative Examples 4 and 5 was charged for one hour under anenvironment of 25° C. and under a constant voltage of 4.2V, followed bydischarging the secondary battery under a low current of 0.2 A to obtaina discharge capacity of 0.2 A. Also, after charged under the sameconditions, the nonaqueous electrolyte secondary battery was dischargedunder a high current of 2 A to measure the discharge capacity of 2 A. Aratio of the 2 A discharge capacity to the 0.2 A discharge capacity wasobtained from the experimental data thus obtained. Further, acharge-discharge cycle test was conducted by repeatedlycharging-discharging the nonaqueous electrolyte secondary battery suchthat the secondary battery was charged under the conditions given above,followed by discharging the secondary battery under a current of 600 mAuntil the battery voltage was lowered to 1.5V. The number ofcharge-discharge cycles that were performed before the battery capacitywas lowered to 800 of the initial capacity was measured to determine thecharge-discharge cycle life. Tables 5 and 6 show the experimental data.

TABLE 1 Average particle Specific diameter surface of area of negativenegative Density Porosity Negative electrode electrode of of electrodeactive active negative negative Ball Stirring Positive electrodeNonaqueous active material material electrode electrode diameter Timeactive material electrolyte material (μm) (m²/g) (g/cm³) (%) (mm)(minutes) Comparative LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂5.84 2.1 2.2 25.6 1 30 Example 1 EC/GBL(1:1) Example 1LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.1 110 EC/GBL(1:2) Example 2 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.4 33.5 1 30 EC/GBL(1:2) Example 3LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 33.6 130 EC/GBL(1:2) Example 4 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.2 1 30 EC/GBL(1:2) Example 5LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 31.9 130 EC/GBL(1:2) Example 6 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.4 31.1 1 30 EC/GBL(1:2) Example 7LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.8 130 EC/GBL(1:2) Example 8 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.4 34.7 1 30 EC/GBL(1:2) Example 9LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 33.3 130 EC/GBL(1:2) Example 10 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.9 1 30 EC/GBL(1:2) Example 11LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 34.7 130 EC/GBL(1:2) Example 12 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.4 33.4 1 30 EC/GBL(1:2) Example 13LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.0 130 EC/GBL(1:2)

TABLE 2 Average particle Specific diameter surface of area of negativenegative Density Porosity Negative electrode electrode of of electrodeactive active negative negative Ball Stirring Positive electrodeNonaqueous active material material electrode electrode diameter Timeactive material electrolyte material (μm) (m²/g) (g/cm³) (%) (mm)(minutes) Example 14 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ MEI/Li/BF₄ Li₄Ti₅O₁₂0.82 10.4 2.4 32.0 1 30 Example 15 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ ammoniumLi₄Ti₅O₁₂ 0.82 10.4 2.4 32.0 1 30 ion/Li/BF₄ Example 16 LiCoO₂ 1.5MLiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.0 1 30 EC/GBL(1:2) Example 17 LiFePO₄1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.0 1 30 EC/GBL(1:2) Example 18LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1M LiPF₆- Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.0 1 30EC/DEC(1:2) Example 19 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.62 21.6 2.3 37.4 1 30 EC/GBL(1:2) Example 20LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.41 35.2 2.2 39.6 130 EC/GBL(1:2) Comparative LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.02 70.4 1.6 44.0 1 30 Example 2 EC/GBL(1:3) Example 21LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- FeS 0.9 8.0 3.6 32.0 1 30EC/GBL(1:2) Example 22 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₂Ti₃O₇0.92 5.4 2.4 33.4 1 30 EC/GBL(1:2) Example 23LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- TiO₂based 0.22 48.9 2 39.8 1 30EC/GBL(1:2) Example 24 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-TiO₂based 0.12 50.0 1.8 39.8 1 30 EC/GBL(1:2) ComparativeLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- TiO₂based 0.12 50.0 1.6 42.1 130 Example 3 EC/GBL(1:3) Comparative LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5MLiBF₄- Graphite 3.4 20.0 1.4 32.0 1 30 Example 4 EC/GBL(1:2)

TABLE 3 Average particle Specific diameter surface of area of negativenegative Density Porosity Negative electrode electrode of of electrodeactive active negative negative Ball Stirring Positive electrodeNonaqueous active material material electrode electrode diameter Timeactive material electrolyte material (μm) (m²/g) (g/cm³) (%) (mm)(minutes) Example 25 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂0.82 10.4 2.2 40.1 5 30 EC/GBL(1:2) Example 26LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.0 110 EC/GBL(1:2) Example 27 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.4 31.9 5 10 EC/GBL(1:2) Example 28LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.4 32.00.5 30 EC/GBL(1:2) Example 29 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.3 37.1 3 60 EC/GBL(1:2) Example 30LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Li₄Ti₅O₁₂ 0.82 10.4 2.2 39.8 15 EC/GBL(1:2) Example 31 LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄-Li₄Ti₅O₁₂ 0.82 10.4 2.0 41.2 3 60 EC/GBL(1:2) ComparativeLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ 1.5M LiBF₄- Graphite 0.83 10.1 1.3 31.9 130 Example 5 EC/GBL(1:2)

TABLE 4 [0.01~0.2 μm] [0.003~0.02 μm] Cycle Spe- Spe- Spe- Spe- Capacitylife cific cific cific cific retention (the Specific Specific pore porepore pore ratio number pore pore Mode volume surface Mode volume surfaceMode 0.2 A during of volume surface diameter The in area in diameter inarea in diameter dis- 2 A charge- in area in of num- negative negativeof negative negative of charge discharge dis- negative negative negativeber elec- elec- negative elec- elec- negative ca- capacity chargeelectrode electrode electrode of trode trode electrode trode trodeelectrode pacity operation oper- (mL/g) (m²/g) (μm) peaks (mL/g) (m²/g)(μm) (mL/g) (m²/g) (μm) (mAh) (%) ations) Comparative 0.0972 2.08 0.2651 0.0803 2.01 0.265 — — — 580 32 250 Example 1 Example 1 0.1474 6.120.155 2 0.1012 6.04 0.155 0.0001 0.10 0.0081 590 90 600 Example 2 0.28808.10 0.105 2 0.1670 7.85 0.105 0.0005 0.26 0.0086 600 91 610 Example 30.2668 7.23 0.095 2 0.1422 7.13 0.095 0.0002 0.13 0.0085 600 90 630Example 4 0.2597 7.17 0.092 2 0.1401 7.11 0.092 0.0003 0.06 0.0083 60092 580 Example 5 0.2527 7.47 0.093 2 0.1409 7.17 0.093 0.0006 0.300.0094 600 91 600 Example 6 0.2600 7.27 0.097 2 0.1451 7.04 0.097 0.00050.23 0.0075 600 90 600 Example 7 0.2547 7.33 0.096 2 0.1361 7.14 0.0960.0003 0.17 0.0084 600 91 590 Example 8 0.2830 8.24 0.091 2 0.1469 8.060.091 0.0003 0.14 0.0084 600 92 600 Example 9 0.2833 8.06 0.090 2 0.13837.90 0.090 0.0003 0.13 0.0084 600 91 620 Example 10 0.2632 7.86 0.097 20.1425 7.71 0.097 0.0002 0.13 0.0085 600 90 610 Example 11 0.2830 7.700.097 2 0.1401 7.40 0.097 0.0006 0.27 0.0100 600 90 590 Example 120.2731 8.00 0.088 2 0.1311 7.71 0.088 0.0006 0.27 0.0100 600 90 600Example 13 0.2586 7.77 0.096 2 0.1393 7.58 0.096 0.0005 0.19 0.0098 60091 610

TABLE 5 [0.01~0.2 μm] Spe- Spe- Spe- Spe- Capacity cific cific Modecific cific Mode [0.003~0.02 μm] retention Cycle pore pore diam- porepore di- Specific Specific ratio life volume surface eter volume surfaceameter pore pore Mode during (the in area in of The in area in of volumesurface diameter 0.2 A 2 A number negative negative negative num-negative negative negative in area in of dis- discharge of elec- elec-elec- ber elec- elec- elec- negative negative negative charge capacitycharge- trode trode trode of trode trode trode electrode electrodeelectrode capacity operation discharge (mL/g) (m²/g) (μm) peaks (mL/g)(m²/g) (μm) (mL/g) (m²/g) (μm) (mAh) (%) operations) Example 14 0.25867.77 0.096 2 0.1393 7.58 0.096 0.0005 0.19 0.0098 600 78 450 Example 150.2586 7.77 0.096 2 0.1393 7.58 0.096 0.0005 0.19 0.0098 600 82 500Example 16 0.2586 7.77 0.096 2 0.1393 7.58 0.096 0.0005 0.19 0.0098 60092 600 Example 17 0.2586 7.77 0.096 2 0.1393 7.58 0.096 0.0005 0.190.0098 600 80 800 Example 18 0.2586 7.77 0.096 2 0.1393 7.58 0.0960.0005 0.19 0.0098 600 80 600 Example 19 0.3374 16.87 0.050 2 0.165015.93 0.051 0.0021 0.91 0.0100 600 94 650 Example 20 0.3921 26.84 0.0182 0.1803 25.46 0.020 0.0084 1.22 0.0100 600 96 700 Comparative 1.221160.12 0.009 1 — — — — — — 550 44 200 Example 2 Example 21 0.2190 5.980.130 2 0.1129 5.74 0.130 0.0005 0.23 0.0085 800 88 450 Example 220.2010 6.24 0.113 2 0.1087 6.08 0.113 0.0006 0.16 0.0081 600 84 500Example 23 0.4973 37.90 0.011 2 0.2347 35.86 0.013 0.0100 1.91 0.0100700 92 480 Example 24 0.6218 39.11 0.010 2 0.3425 37.01 0.011 0.01602.43 0.0130 680 90 400 Comparative 1.0284 44.24 0.010 1 — — — — — — 60038 150 Example 3 Comparative 0.2580 7.62 0.100 1 0.1274 7.60 0.098 — — —600 85 20 Example 4

TABLE 6 Cycle Spe- Spe- [0.003~0.02 μm] Capacity life cific cific Mode[0.01~0.2 μm] Mode retention (the pore pore diam- Specific SpecificSpecific Specific diam- ratio number volume surface eter pore pore Modepore pore eter during of in area in of The volume surface diametervolume surface of 0.2 A 2 A charge- negative negative negative num- inarea in of in area in negative dis- discharge dis- elec- elec- elec- bernegative negative negative negative negative elec- charge capacitycharge trode trode trode of electrode electrode electrode electrodeelectrode trode capacity operation oper- (mL/g) (m²/g) (μm) peaks (mL/g)(m²/g) (μm) (mL/g) (m²/g) (μm) (mAh) (%) ations) Example 25 0.4940 60.30.059 2 0.4705 48.9 0.059 0.02 10 0.018 600 91 550 Example 26 0.13846.10 0.169 2 0.1010 6.00 0.169 0.0001 0.10 0.003 590 87 600 Example 270.3200 12.7 0.062 2 0.2625 10.84 0.062 0.0180 1.86 0.02 600 91 560Example 28 0.0598 6.33 0.174 2 0.05 6.21 0.194 0.0001 0.10 0.0080 590 84600 Example 29 0.5981 52.0 0.054 2 0.5 49.1 0.054 0.02 2.73 0.019 600 91570 Example 30 0.1073 5.20 0.170 2 0.0903 5 0.170 0.0001 0.10 0.003 59085 600 Example 31 1.0121 49.8 0.082 2 0.4683 47.0 0.060 0.017 2.21 0.016600 90 590 Comparative 0.1424 6.10 0.153 2 0.1010 6.03 0.153 0.0001 0.100.0081 590 65 15 Example 5

As apparent from the experimental data given in Tables 1 to 6, thenonaqueous electrolyte secondary battery for each of Examples 1 to 31was found to be superior to that for each of Comparative Examples 1 toin charge-discharge cycle characteristics.

Concerning the specific volume of the first pores having a diameter of0.01 to 0.2 μm, the experimental data for Examples 1, 28 and 29 indicatethat the nonaqueous electrolyte secondary battery is excellent in boththe high rate discharge characteristics and the charge-discharge cyclecharacteristics in the case where the specific volume of the first poresformed in the negative electrode falls within a range of 0.05 to 0.5mL/g.

When it comes to the specific surface area of the first pores having adiameter of 0.01 to 0.2 μm, the experimental data for Examples 1, 25 and30 indicate that the nonaqueous electrolyte secondary battery isexcellent in both the high rate discharge characteristics and thecharge-discharge cycle characteristics in the case where the specificsurface area of the pores formed in the negative electrode falls withina range of 5 to 50 m²/g.

When it comes to the mode diameter of the first peak, it can beunderstood by the comparison among Examples 1, 2, 20, 23 and 28 that thenonaqueous electrolyte secondary battery is excellent in both the highrate discharge characteristics and the charge-discharge cyclecharacteristics in the case where the mode diameter of the first peakfalls within a range of 0.01 to 0.2 μm. Particularly, the experimentaldata support that excellent charge-discharge cycle characteristics canbe obtained in the case where the mode diameter of the first peak fallswithin a range of 0.02 to 0.1 μm as in Examples 2 and 20.

Concerning the specific volume of the second pores having a diameter of0.003 to 0.02 μm, the experimental data for Examples 1 and 25 indicatethat the nonaqueous electrolyte secondary battery is excellent in boththe high rate discharge characteristics and the charge-discharge cyclecharacteristics in the case where the specific volume of the secondpores formed in the negative electrode falls within a range of 0.0001 to0.02 mL/g.

When it comes to the specific surface area of the second pores having adiameter of 0.003 to 0.02 μm, the experimental data for Examples 1 and25 indicate that the nonaqueous electrolyte secondary battery isexcellent in both the high rate discharge characteristics and thecharge-discharge cycle characteristics in the case where the specificsurface area of the second pores formed in the negative electrode fallswithin a range of 0.1 to 10 m²/g.

Further, when it comes to the mode diameter of the second peak, it canbe understood by the comparison among Examples 1, 26, and 27 that thenonaqueous electrolyte secondary battery is excellent in both the highrate discharge characteristics and the charge-discharge cyclecharacteristics in the case where the mode diameter of the second peakfalls within a range of 0.003 to 0.02 μm.

Concerning the kind of the negative electrode active material, it hasbeen clarified by the comparison among Examples 1, 21, 22 and 23 thatthe nonaqueous electrolyte secondary battery for each of Examples 1, 22and 23 using a titanium-containing composite oxide as the negativeelectrode active material was superior in the charge-discharge cyclecharacteristics to the nonaqueous electrolyte secondary battery forExample 21 using an iron-based sulfide as the negative electrode activematerial. It should be noted in particular that the nonaqueouselectrolyte secondary battery for each of Examples 1 and 22 using alithium-titanium oxide as the negative electrode active material wasfound to be particularly excellent in the charge-discharge cyclecharacteristics.

Concerning the kind of the positive electrode active material, theexperimental data for Examples 13, 16 and 17 indicate that thenonaqueous electrolyte secondary battery for each of these Examples wasexcellent in both the high rate discharge characteristics and thecharge-discharge cycle characteristics. In the nonaqueous electrolytesecondary battery for Example 13, a lithium-nickel-cobalt-manganesecomposite oxide was used as the positive electrode active material, andin the nonaqueous electrolyte secondary battery for Example 16, alithium-cobalt composite oxide was used as the positive electrode activematerial. It was possible to obtain particularly excellent high ratedischarge characteristics in the nonaqueous electrolyte secondarybattery for each of these Examples 13 and 16. On the other hand, thenonaqueous electrolyte secondary battery for Example 17, in which alithium-phosphorus oxide having an olivine structure was used as thepositive electrode active material, was found to be advantageous interms of the charge-discharge cycle characteristics.

Regarding the kind of the nonaqueous electrolyte, it has been clarifiedby the comparison among Examples 13, 14, 15 and 18 that the nonaqueouselectrolyte secondary battery for each of Examples 13 and 18 in whichnonaqueous electrolyte used contained an organic solvent, is superior inthe charge-discharge cycle characteristics to the nonaqueous electrolytesecondary battery for each of Examples 14 and 15, in which thenonaqueous electrolyte used contained an ionic liquid. In particular,the secondary battery for Example 13 in which the nonaqueous electrolyteused contained GBL was found to be superior in both the high ratedischarge characteristics and the charge-discharge cycle characteristicsto the secondary battery for

Example 18

A negative electrode active material exhibiting a Li ion insertionpotential lower than 0.4V (vs. Li/Li⁺) was used in the battery for eachof Comparative Examples 4 and 5. The negative electrode used in thebattery for Comparative Example 4 exhibited a pore diameter distributionthat did not have a second peak. As a result, the battery forComparative Example 4 was found to have a charge-discharge cycle lifethat was markedly shorter than that for each of Examples 1 to 31. Thenegative electrode used in the battery for Comparative Example 5certainly exhibited the pore diameter distribution substantially equalto that for Example 1. However, the battery for Comparative Example 5was found to be inferior in both the high rate discharge characteristicsand the charged-discharge cycle life.

FIGS. 7 and 8 are graphs each showing the pore diameter distribution asdetermined by mercury porosimetry in respect of the negative electrodeincluded in the nonaqueous electrolyte secondary battery for Example 3.The graph of FIG. 7 shows that the first peak has a mode diameter of0.095 μm (which corresponds to Example 3). FIG. 8 shows in a magnifiedfashion that region of the pore diameter distribution shown in FIG. 7which is in the vicinity of 0.01 μm of the pore diameter. The graph ofFIG. 8 indicates that the second peak has a mode diameter of 0.0085 μm.Incidentally, the pore volume (mL) per gram of the negative electrodeincluding the current collector is plotted on the ordinate of each ofthe graphs shown in FIGS. 7 and 8.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A nonaqueous electrolyte battery, comprising: a positive electrode; anegative electrode including a current collector and a negativeelectrode layer being supported by the current collector, and thenegative electrode layer containing a titanium-based oxide having a Liion insertion potential not lower than 0.4V (vs. Li/Li⁺); and anonaqueous electrolyte; wherein: the negative electrode has a porousstructure; a pore diameter distribution of the negative electrode asdetermined by a mercury porosimetry, which includes a first peak havinga mode diameter falling within a range of 0.01 to 0.2 μm, and a secondpeak having a mode diameter falling within a range of 0.003 to 0.02 μm;a volume of pores having a diameter of 0.01 to 0.2 μm as determined bythe mercury porosimetry is 0.05 to 0.5 mL per gram of the negativeelectrode excluding the weight of the current collector; and a volume ofpores having a diameter of 0.003 to 0.02 μm as determined by the mercuryporosimetry is 0.0001 to 0.02 mL per gram of the negative electrodeexcluding the weight of the current collector.
 2. The nonaqueouselectrolyte battery according to claim 1, wherein a surface area ofpores has a diameter of 0.01 to 0.2 μm as determined by the mercuryporosimetry, which falls within a range of 5 to 50 m² per gram of thenegative electrode excluding the weight of the current collector, and asurface area of pores has a diameter of 0.003 to 0.02 μm as determinedby the mercury porosimetry, which falls within a range of 0.1 to 10 m²per gram of the negative electrode excluding the weight of the currentcollector.
 3. The nonaqueous electrolyte battery according to claim 1,wherein a surface area of pores has a diameter of 0.01 to 0.2 μm asdetermined by the mercury porosimetry, which falls within a range of 7to 30 m² per gram of the negative electrode excluding the weight of thecurrent collector, and a surface area of pores has a diameter of 0.003to 0.02 μm as determined by the mercury porosimetry, which falls withina range of 0.2 to 2 m² per gram of the negative electrode excluding theweight of the current collector.
 4. The nonaqueous electrolyte batteryaccording to claim 1, wherein the negative electrode has a pore volumeas determined by the mercury porosimetry, which falls within a range of0.1 to 1 mL per gram of the negative electrode excluding the weight ofthe current collector.
 5. The nonaqueous electrolyte battery accordingto claim 1, wherein the negative electrode has a pore volume asdetermined by the mercury porosimetry, which falls within a range of 0.2to 0.5 mL per gram of the negative electrode excluding the weight of thecurrent collector.
 6. The nonaqueous electrolyte battery according toclaim 1, wherein the mode diameter of the first peak of the porediameter distribution falls within a range of 0.02 to 0.1 μm.
 7. Thenonaqueous electrolyte battery according to claim 1, wherein the modediameter of the second peak of the pore diameter distribution fallswithin a range of 0.005 to 0.015 μm.
 8. The nonaqueous electrolytebattery according to claim 1, wherein the volume of pores has a diameterof 0.01 to 0.2 μm as determined by the mercury porosimetry, which fallswithin a range of 0.1 to 0.3 mL per gram of the negative electrodeexcluding the weight of the current collector.
 9. The nonaqueouselectrolyte battery according to claim 1, wherein the volume of poreshas a diameter of 0.003 to 0.02 μm as determined by the mercuryporosimetry, which falls within a range of 0.0005 to 0.01 mL per gram ofthe negative electrode excluding the weight of the current collector.10. The nonaqueous electrolyte battery according to claim 1, wherein thetitanium-based oxide is formed of particles having an average particlediameter not larger than 1 μm.
 11. The nonaqueous electrolyte batteryaccording to claim 1, wherein the current collector is formed of analuminum foil or an aluminum alloy foil.
 12. The nonaqueous electrolytebattery according to claim 11, wherein each of the aluminum foil and thealuminum alloy foil has an average crystal grain size not larger than 50μm.
 13. The nonaqueous electrolyte battery according to claim 1, whereinthe positive electrode contains a compound represented byLi_(a)Ni_(b)Co_(c)Mn_(d)O₂, where 0≦a≦1.1, 0.1≦b≦0.5, 0≦c≦0.9, and0.1≦d≦0.5.
 14. The nonaqueous electrolyte battery according to claim 1,wherein the nonaqueous electrolyte contains at least two kinds ofsolvents selected from the group consisting of propylene carbonate,ethylene carbonate, and γ-butyrolactone.
 15. The nonaqueous electrolytebattery according to claim 1, wherein the titanium-based oxide is atleast one selected from the group consisting of TiO₂ and a metalcomposite oxide containing Ti and at least one element selected from thegroup consisting of P, V, Sn, Cu, Ni, Co, and Fe.
 16. The nonaqueouselectrolyte battery according to claim 15, wherein the metal compositeoxide is at least one selected from the group consisting of TiO₂—P₂O₅,TiO₂—P₂O₅—SnO₂ and TiO₂—P₂O₅-MeO, where Me is at least one elementselected from the group consisting of Cu, Ni, Co, and Fe.
 17. Thenonaqueous electrolyte battery according to claim 1, further comprising:a case having a first sealing section formed at one edge portion and asecond sealing section formed at another edge portion opposite to saidone edge portion; a positive electrode terminal including a tip portionwithdrawn to an outside via the first sealing section of the case; and anegative electrode terminal including a tip portion withdrawn to theoutside via the second sealing section of the case.
 18. A battery packcomprising the nonaqueous electrolyte battery according to claim
 1. 19.A vehicle comprising a battery pack defined in claim 1.